Digital Post-Distortion for Multi-Layer MIMO-OFDM

Abstract

In this letter, we propose a new digital post-distortion (DPoD) technique for precoded multi-layer orthogonal frequency division multiplexing (OFDM) systems, in order to enhance the received signal error vector magnitude (EVM) under heavily nonlinear power amplifiers (PAs) in the transmitter. The proposed multi-layer digital post-inverse (ML-DPoI) builds on layer-or stream-level nonlinear distortion modeling and corresponding signal processing at receiver, combined with true reference signal based model parameter estimation allowing to operate without any prior knowledge of the transmit precoder or PA behavior. Numerical evaluations with dual-layer rank-2 transmission in 5G New Radio (NR) uplink context with standard-compatible physical-layer transmit waveform show that despite heavily nonlinear PA units, the received signal EVM can be reliably enhanced – even in the case of very high modulation order such as 256-QAM per transmit stream. These results pave the way towards improved power-efficiency and sustainability in future networks, especially at millimeter-wave bands, where transmitter power-efficiency is known to be a major implementation challenge.