Distortion cancellation precoding for OFDM-SDMA downlink with nonlinear power amplifiers

In this work we consider an OFDM-SDMA downlink with a real life, nonlinear Power Amplifier (PA). It is well known that a nonlinear PA produces nonlinear distortions. We propose a novel iterative algorithm based on Zero Forcing (ZF) precoding to cancel the nonlinear distortions seen at the mobile devices while preserving the interference-free reception due to ZF. The proposed algorithm also keeps the out-of-band radiation of the transmitted signals low, in order to satisfy spectral purity requirements. For a low Back-Off (BO) scenario, where the nonlinear distortions are strong, the proposed algorithm shows a much lower Symbol Error Rate (SER) and much higher power efficiency than the well known ZF-SDMA with a real life PA.