Low complexity hybrid wideband beamforming for millimeter-wave massive MIMO-OFDM systems

In mmWave massive multiple-input multiple-output (MIMO) communication systems, the extension of low-complexity narrowband precoding schemes to be operated on wideband systems under frequency-selective channels remains an important challenge at the current time. This paper investigates a low complexity wideband hybrid precoding scheme for mmWave massive MIMO multicarrier systems under a single-user, fully-connected hybrid architecture. We show that the radio frequency (RF) pre-coding/combining vectors can be directly derived from the eigenvectors of the optimal fully-digital covariance matrix over all subcarriers in order to maximize the sum rate of spectral efficiency. We also suggest a new method that iteratively reduces the residual error between the covariance matrix and the sum of products of precoding matrices over all the subcarriers to improve the performance in the case where the number of RF chains is higher than the number of streams. The results of the simulation show that the proposed schemes' complexity is low compared to the present methods, and their performance can almost reach the upper bound achieved by the optimal full-baseband design.