This paper describes a complete digital radio system model which takes into account the effects of most degradations due to channel conditions and equipment imperfections. System parameters which are taken into consideration include, but are not limited to, the following: modulator imbalance, filter frequency responses, power amplifier nonlinearities, carrier and symbol timing recovery loops, and synthesizer phase noise. The parameters for each module in the radio can be varied, and the end-to-end performance computed. Furthermore, a novel semianalytic method is developed for the purpose of speeding up the simulation leading to the calculation of the bit error rate (BER) versus E/sub b//N/sub o/ for the radio model. This novel technique, when compared with classical semianalytic methods, provides 1 dB improvement in the accuracy of the simulation results. The model accurately predicts the radio performance as measured by BER versus E/sub b//N/sub o/, dispersive fade margin, transmitted frequency spectrum, and transient acquisition responses. Simulation results for 16 QAM and OQPSK systems were compared to measurements on two physical radios. The accuracy of the simulation results was found to be within 0.1 dB in E/sub b//N/sub o/ at a BER of 10/sup -6/ without the RF portions and between 0.2 and 0.45 dB for a complete radio system.