Abstract
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.
Highlights
Massive multiple-input multiple-output (MIMO) has emerged as one of the most disruptive technologies for 5G wireless networks with the potential of enhancing system performance in terms of spectral efficiency (SE) and energy efficiency (EE) significantly [1]–[8]
It shows that the rate performance of LOS-equal-gain transmission (EGT) precoding is better than that of maximum-ratio transmission (MRT) precoding with Rician fading channel in distributed massive MIMO (DM-MIMO) system because of the fact that the LOS component-based EGT (LOS-EGT) precoding requires the least amount of pilot overhead and is free from pilot contamination (PC)
Closed-form expressions of the lower bound on the achievable DL rate were obtained for the MRT and LOS component-based EGT precoding schemes
Summary
Massive multiple-input multiple-output (MIMO) has emerged as one of the most disruptive technologies for 5G wireless networks with the potential of enhancing system performance in terms of spectral efficiency (SE) and energy efficiency (EE) significantly [1]–[8]. The tractable but accurate closed-form lower-bound expressions which contribute to system performance analysis and establishing various power scaling properties are derived for the DL achievable rate of MRT and LOS-EGT processing under Rician fading in DM-MIMO systems, respectively. It is shown that with LOS-EGT precoding and under Rician fading in DM-MIMO systems, the DL data transmit power of each user can be scaled down by N −p (0 ≤ p ≤ 1), while the achievable rate approaches infinity if 0 ≤ p < 1 and maintains an asymptotically unchanged user rate otherwise when the number of RAUs antennas N grows unlimited. The fast fading channel vector between the users and the RAUs in the same cell is modeled to consist of two parts, namely a deterministic component corresponding to the LOS path and a Rayleigh-distributed random component which accounts for the scattered signals.
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