Detailed analysis of the impact of the distortion due to nonlinear amplifiers on BER performance

This paper presents a detailed analysis of the distortion effects of the power amplifier nonlinearity on the bit error rate (BER) performance of a band limited digitally modulated signal present at the amplifier input. Previous analyses of such distortion effects are mainly concerned with the total distortion power present at the amplifier output and in some cases present results on the amplifier output power spectral density. However, the power spectral density of the total signal in the fundamental zone at the amplifier output does not lend itself to the BER analysis. In the case where the total distortion power is known, one may assume that the distortion is independent of the signal of interest and has a Gaussian probability density function and thereby add the distortion power to the receiver noise power in order to obtain the BER. While such a simplified approach may be valid in some cases, such assumptions do not apply to the case of a single band limited digital signal at the amplifier input, which is the case of interest here. In fact this paper shows that in this case the distortion is neither Gaussian nor independent of the signal. Thus the BER analysis in such a case becomes relatively difficult. This paper presents a semi-analytical approach to the evaluation of the BER in the presence of both the amplifier distortion and the receiver noise. It is shown in the paper that the conditional probability density function of the amplifier distortion can be modeled by a sum of Gaussian distributions whereby the BER in the presence of both the amplifier distortion and receiver noise can be expressed in terms of a weighted sum of Q-functions.