Downlink Transmission of Multicell Distributed Massive MIMO With Pilot Contamination Under Rician Fading

In this paper, we investigate the spectral efficiency (SE) of a multicell downlink (DL) distributed massive MIMO (DM-MIMO) system with pilot contamination operating over Rician fading channels in which each remote access unit (RAU) is equipped with a large number of distributed massive antenna arrays, while each user has a single antenna. In contrast to many previous works about DM-MIMO systems, the channel between users and the RAUs antennas in the same cell is modeled to be Rician fading, which is general for the 5G scenarios like Internet of Things. We explore maximum-ratio transmission (MRT) and line-of-sight (LOS) component-based equal-gain transmission (EGT) under imperfect channel state information. The tractable, but accurate closed-form expressions for the lower bounds of the achievable rate are derived for the MRT and the LOS component-based EGT over Rician fading channels in the DM-MIMO systems. Based on the obtained closed-form expressions, various power scaling laws concerning DL data transmit power and pilot transmit power are analyzed in detail. Numerical results are used to corroborate that these approximations are asymptotically tight, but accurate for systems. They also show that employing the LOS component-based EGT processing is more preferable than the MRT processing for DM-MIMO systems in conditions having a large number of RAU antennas and stronger LOS scenarios. Finally, the simulation results further show that when the number of all antennas for RAUs is fixed, the better SE performance can be obtained with more RAUs.