Nonlinear amplifier effects on clipped-filtered multicarrier signals

The clipping-filtering method is a simple and frequently used in practice technique for reducing envelope fluctuations in multicarrier systems. When analysing systems that use clipping-filtering, very often a linear amplification is assumed. Meanwhile, a nonlinear amplifier inserts additional distortions into the clipped-filtered multicarrier signal. The cascade of the clipper-filter-nonlinear amplifier results in a nonlinear system with memory. The author studies both time-domain and frequency domain effects in this system. It is shown that while aggravating the total degradation in the system (almost for all values of the clipping ratio), the procedure of clipping-filtering provides a reduction of the out-of-band power emission after a nonlinear amplification. The author studies the structure of the clipped-filtered-amplified signal and proves that the signal constellation after this procedure is similar to that obtained after memoryless nonlinear processing, i.e. the observed signal is an attenuated version of the useful signal corrupted by Gaussian-like noise. Moreover, even under severe clipping and the working points of the amplifier close to the saturation (i.e. small values of the amplifier back-offs), Bussgang´s theory can be approximately used for the prediction of distortions in the above scheme.