A new method is applied to perform, by Harmonic Balance (HB) techniques, the simulation of a GaN Doherty Power Amplifier (DPA) driven by carrier Random-Modulated (RM) signals. This article presents an example (16-QAM) of a driving random modulated voltage generated in the frequency-domain and the software-defined demodulation of the output signal of the DPA implemented with optimal matched filters to respect the Nyquist criteria. It allows the extraction of all the linearity and power metrics performances at design circuit level in the time and frequency-domains. For instance, dynamic power and linearity (Adjacent Channel Power Ratio (ACPR), Error Vector Magnitude (EVM)) performances are calculated. The simulated dynamic results are shown and compared to the measured results obtained on a specific THA-based time-domain calibrated test-bench developed in our laboratory. The Quasi-MMIC DPA under test is driven by a 3.5 GHz carrier frequency modulated with a 16-QAM signal for two different symbol rates.