Low-Rate Cascaded Parallel Digital Predistortion for Sub-6-GHz 400-MHz Signal Transmission

Abstract

This article proposes a novel, low-rate digital predistortion (DPD) for sub-6-GHz 400-MHz modulated signal transmission. In this model, a low-rate input signal is concurrently fed into multiple parallel cascaded model branches to generate the low-rate predistorted signal. Each branch contains: a dual-function finite impulse response (FIR) filter for interpolation and memory effect compensation, multiple parallel Volterra series-based submodels that are selectively activated based on the current input state and are optimized in complexity by a pruning algorithm, and low-rate filters. Additionally, a model parameter extraction method is introduced for this model. Based on this model, a high-precision DPD system can be obtained with low system processing rates. Experimental validation was performed using 5G new radio (NR) signals with 400-MHz modulation bandwidth on a 3.4–3.8-GHz gallium nitride (GaN) Doherty power amplifier (PA) at low system processing rates of 983 and 491 MSPS, respectively. Measurement results demonstrated that the proposed technique achieves good performance with lower complexity than existing models, with a normalized mean-square error (NMSE) and an adjacent channel power ratio (ACPR) of approximately −41 dB and −46 dBc at 983 MSPS, respectively, and an NMSE of approximately −40 dB at 491 MSPS.