PAPR Reduction in OFDM With Hybrid Beamforming—A Less Explored Problem

The time-domain signal in orthogonal frequency division multiplexing (OFDM) has a large peak-to-average power ratio (PAPR). Most existing solutions for this problem are designed for OFDM systems operating with a fully-digital MIMO architecture. However, these solutions cannot be used for an OFDM system operating with a hybrid beamforming architecture. Therefore, in this work we address PAPR reduction in OFDM with hybrid beamforming. We propose to transmit a PAPR reduction signal along with the precoded information signal. For an efficient design of the PAPR reduction signal, we propose to use extra radio frequency (RF) chains. The design of the PAPR reduction signal and the analog beamformers corresponding to the extra RF chains, is written as a constrained optimization problem. An iterative algorithm based on successive convex approximation is proposed to solve the optimization problem. We show that the proposed technique achieves a considerable end-to-end performance gain in the presence of a non-linear power amplifier.