Nonlinear channels: predistortion or enhanced detection?

Using a union bound on the error probability of optimal receivers for nonlinear channels, this work points out important factors affecting the error performance in the simple case of M-ary pulse amplitude modulation (M-PAM) with no intersymbol interference and unlimited transmission bandwidth. The performance is compared to that obtainable when the nonlinear device is perfectly linearized under a peak power constraint. Considered nonlinearities include third-order polynomials and soft-limiters. Simulation results are in good agreement with the derived theoretical bounds. The analysis suggests that margins for improved performance exist, with respect to the performance obtainable by perfect linearization, when the cardinality of the signal set is not large (e.g., 4- or 8-PAM) and the nonlinearity is not severely saturated.