Digital Post-Distortion for DFT-s-OFDM

Abstract

In this paper, we propose and describe a novel digital post-distortion (DPoD) method for enhancing the received signal error vector magnitude (EVM) in discrete Fourier transform spread orthogonal frequency-division multiplexing (DFT-s-OFDM) systems when operating under largely nonlinear transmitter power amplifiers (PAs). The proposed method builds on nonlinear distortion modeling and cancellation through memory polynomials, complemented with practical demodulation reference signal (DMRS) based parameter estimation. Importantly, a new DMRS configuration is proposed such that the enhanced DMRS envelope distribution closely approximates that of the actual data-bearing symbols, thus allowing for accurate DPoD parameter estimation. Comprehensive numerical evaluations are provided in 5G New Radio (NR) uplink context at the 28 GHz millimeter-wave band, with standard-compliant evaluation assumptions. The results show that efficiently improving the received signal EVM is feasible, even when operating under harsh nonlinear distortion and high modulation orders such as 256-QAM or even 1024-QAM.