FFT-Based Limited Subband Digital Predistortion Technique for Ultra Wideband 5G Systems

Parallel subband digital predistortion (DPD) has emerged as a promising approach for linearizing power amplifiers (PA) in wireless communication systems. This solution has the advantage of relaxing the bandwidth constraints on the feedback path analog to digital converter (ADC) which digitizes the PA distorted output which may spread over several hundreds MHz in the latest generations of mobile communications. However, the subband approach still has some limitations such as signal reconstruction and subband aliasing which limits its implementation on a wide scale. In this paper, an FFT-Based DPD technique that enables to compute the predistorter without interpolating signals is presented. Thanks to the frequency domain approach, the subband signals can be combined easily to compute the fullband predistorter directly. Moreover, the proposed technique offers the possibility of selecting specific frequency bins for the computation. In particular, the subband edges can be ignored which will result in relaxed bandwidth constraints and selectivity for the subband ADCs. Simulations show that the proposed FFT based subband DPD performs as good as the conventional time domain least-square approach even while excluding up to 13% of the FFT bins at the band edges.