Low complexity hybrid precoding in finite dimensional channel for massive MIMO systems

Massive multiple-input multiple-output (MIMO) is an emerging technology for future wireless networks, scaling up conventional MIMO to an unprecedented number of antennas at base stations. Such a large antenna array has the potential to make the system achieve high channel capacity and spectral efficiency, but it also leads to high cost in terms of hardware complexity. In this paper, we consider a finite dimensional channel model in which finite distinct directions are applied with M angular bins. In massive multi-user MIMO systems, a hybrid precoding method is proposed to reduce the required number of radio frequency (RF) chains at the base station, employing a single antenna per mobile station. The proposed precoder is partitioned into a high-dimensional RF precoder and a low-dimensional baseband precoder. The RF precoder is designed to obtain power gain with phase-only control and the baseband precoder is designed to facilitate multi-stream processing. For realistic scenarios, we consider the situation where the RF phase control is quantized up to B bits of precision. Furthermore, an upper bound on spectral efficiency is derived with the proposed precoding scheme. The simulation results show that hybrid precoding achieves desirable performance in terms of spectral efficiency, which approaches the performance of zero-forcing precoding.