Adaptive Linearization through Narrowband Feedback

An adaptive predistorter (PD) is an effective technique to compensate for the nonlinear distortion of power amplifiers. To enable broadband communications, the bandwidth of communication systems has had to continuously increase. With these increases in bandwidth, frequency distortions due to limitations in the bandwidth of the PD´s building blocks can no longer be ignored. Such distortions are important factors that define a PD´s linearization performance. In this study, we investigated the adaptive PD performance degradation caused by bandwidth restrictions in the feedback (FB) path. Employing a newly proposed graphical approach which we confirmed by computer simulations. We show that achieving PD linearization with narrowband FB strongly depends on the PD´s architecture and the FB path bandwidth. Finally, we make practical recommendations regarding the implementation of adaptive PDs having memoryless and memory polynomial architectures that depend on the available FB path bandwidth.