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 perfo rmance evaluation in M-ary quadrature amplitude modulation (M-QAM) ort hogonal frequency-division multiplexing (OFDM) digital radio systems i n the presence of nonlinear distortions caused by high-power amplifier s (HPA's). The present analysis is carried out considering an additive white Gaussian noise (AWGN) transmission channel, It is shown that, i n the case of an OFDM system with a large number of subcarriers, the d istortion on the received symbol caused by the amplifier can be modele d, 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, I n practice, the simulation aspect is only used to estimate means and v ariances of the ''nonlinear noise.'' Such estimated parameters are sub sequently used to evaluate analytically the system bit-error rate (BER ) using an expression, which takes into account both AWGN and ''nonlin ear 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 c ompared with a classical semianalytical approach. This is especially t rue when low BER values (<10(-4)) have to be estimated, The proposed p rocedure will be applied to evaluate M-QAM-OFDM performance in the pre sence of nonlinear distortions caused by traveling-wave tube (TWT) and solid-state-power (SSP) amplifiers.