A hybrid analytical-simulation procedure for performance evaluation in M-QAM-OFDM schemes in presence of nonlinear distortions

This paper presents a hybrid analytical-simulation procedure for performance evaluation in M-ary quadrature amplitude modulation (M-QAM) orthogonal frequency-division multiplexing (OFDM) digital radio systems in the presence of nonlinear distortions caused by high-power amplifiers (HPA's). The present analysis is carried out considering an additive white Gaussian noise (AWGN) transmission channel, It is shown that, in the case of an OFDM system with a large number of subcarriers, the distortion on the received symbol caused by the amplifier can be modeled, with good approximation, as a "Gaussian nonlinear noise" added to the received symbol, This important result allows a hybrid analytical-simulation approach to solve the problem of performance evaluation, In practice, the simulation aspect is only used to estimate means and variances of the "nonlinear noise." Such estimated parameters are subsequently used to evaluate analytically the system bit-error rate (BER) using an expression, which takes into account both AWGN and "nonlinear noise" effects. The advantage of the proposed method lies in the strongly reduced computational time, In fact, an accurate estimate of the "nonlinear noise" parameters requires only few iterations when compared with a classical semianalytical approach. This is especially true when low BER values (<10(-4)) have to be estimated, The proposed procedure will be applied to evaluate M-QAM-OFDM performance in the presence of nonlinear distortions caused by traveling-wave tube (TWT) and solid-state-power (SSP) amplifiers.