Linearization through Narrowband Feedback: Problems and Solutions

An adaptive predistorter is an effective technique to compensate for the nonlinear distortion of power amplifiers. To enable broadband communications, the bandwidth of communication systems has been continuously increased. With these increases in bandwidth, frequency distortions due to limitations in the bandwidth of the predistorter´s building blocks can no longer be ignored. Such distortions are important factors that deteriorate a predistorter´s linearization performance. Two main problems directly related with linearization through the narrow feedback path have been the subject of investigation in this study: predistorter´s performances degradation due to feedback signal bandwidth restrictions and selection of appropriate predistorter architecture suitable for the linearization through narrowband feedback path. Also, in this study we propose a new predistorter architecture based on the inverse modeling for the power amplifier model that is robust against feedback signal bandwidth restrictions. Simulation and experimental results show that with the proposed predistorter architecture, the required feedback signal bandwidth can be reduced approximately to 1.15 times of the transmitting signal bandwidth with minimal degradations in the linearization performances.