Single-user MIMO versus multi-user MIMO in distributed antenna systems with limited feedback

Abstract

This article investigates the performance of cellular networks employing distributed antennas in addition to the central antennas of the base station. Distributed antennas are likely to be implemented using remote radio units, which is enabled by a low latency and high bandwidth dedicated link to the base station. This facilitates coherent transmission from potentially all available antennas at the same time. Such distributed antenna system (DAS) is an effective way to deal with path loss and large-scale fading in cellular systems. DAS can apply precoding across multiple transmission points to implement single-user MIMO (SU-MIMO) and multi-user MIMO (MU-MIMO) transmission. The throughput performance of various SU-MIMO and MU-MIMO transmission strategies is investigated in this article, employing a Long-Term evolution (LTE) standard compliant simulation framework. The previously theoretically established cell-capacity improvement of MU-MIMO in comparison to SU-MIMO in DASs is confirmed under the practical constraints imposed by the LTE standard, even under the assumption of imperfect channel state information (CSI) at the base station. Because practical systems will use quantized feedback, the performance of different CSI feedback algorithms for DASs is investigated. It is shown that significant gains in the CSI quantization accuracy and in the throughput of especially MU-MIMO systems can be achieved with relatively simple quantization codebook constructions that exploit the available temporal correlation and channel gain differences.

Distributed Hybrid Precoding for Indoor Deployments Using Millimeter Wave Band

“…Furthermore, path 2 Mobile Information Systems loss differences between the distributed antennas become significant in DAS, so techniques selecting only a subset of the antennas for transmission can bring large benefits to the system [8]. The performance of SU and MU MIMO techniques in DAS with different degrees of cooperation among RAUs is analyzed in [4,9]. Both works conclude that large performance gains are achieved when antenna selection schemes are applied.…”

Robust channel quality indicator reporting for multi-carrier and multi-user systems

“…In [24], the authors propose a joint framework for relay selection and resource allocation for OFDMA based cooperative system that uses outdated (due to feedback delay) CQIs. A general framework for studying the impact of imperfect channel knowledge on multi-user MIMO distributed antenna system has been demonstrated in [25] whereas the comparative analysis of for distributed antenna MIMO system in the context of single-user and multi-user scenarios with limited feedback has been performed in [26]. A low computational-complexity cross-layer approach for maximizing the downlink throughput of a system with coordinating base stations and imperfect and partial feedback is proposed in [27].…”

“…The impact of imperfect CQI on the performance degradation of multi-carrier systems at the resource allocation level at the base station has been well studied (e.g., [15][16][17][18][19][20][21][22][23][24][25][26][27]). In [15], analysis of OFDMA throughput under the assumption of imperfect CQI and un-coded modulation has been performed and a close form expression for the average throughput has been derived.…”

Robust full-dimension MIMO transmission based on limited feedback angular-domain CSIT

“…In this equation, we again utilized the phase independence of different specular components as in the steps from (19) to (20). We next apply an eigen-decomposition to the sum of the specular components:…”

“…In MIMO transmission in general, and especially when considering multipoint communication, CSIT is an essential ingredient. CSIT for downlink transmission is commonly obtained either from uplink measurements using dedicated uplink pilot signals [18,19] or from limited channel state information (CSI) feedback from the users [20][21][22]. We consider frequency division duplex (FDD) transmission in this paper, where CSIT is provided via feedback from the users over dedicated limited capacity feedback links.…”