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Field Experimental Evaluation of Null Control Performance of MU-MIMO Considering Smart Vertical MIMO in LTE-Advanced Downlink under LOS Dominant Conditions

Yuki INOUE
Daiki TAKEDA
Keisuke SAITO
Teruo KAWAMURA
Hidehiro ANDOH

Publication
IEICE TRANSACTIONS on Communications   Vol.E97-B    No.10    pp.2136-2144
Publication Date: 2014/10/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.E97.B.2136
Type of Manuscript: Special Section PAPER (Special Section on Recent Progress in Measurement and Design Techniques on Antennas, Propagation and Wireless Systems)
Category: 
Keyword: 
LTE-Advanced,  multi-user MIMO,  Smart Vertical MIMO,  field experiment,  spatial correlation,  null control,  

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Summary: 
The performance in terms of the user separation of multi-user multiple-input multiple-output (MU-MIMO) depends on not only the spatial correlation but also the location of the mobile stations (MSs). In order to take into account the performance in terms of the user separation, we need to consider the granularity of the beam and null width of the precoded antenna pattern in addition to the spatial correlation to determine the base station (BS) antenna configuration. In this paper, we propose Smart Vertical MIMO (SV-MIMO) as the best antenna configuration that achieves both spatial correlation and granularity of the beam and null width of the precoded antenna pattern. We evaluate SV-MIMO in a field experiment using a downlink 4-by-2 MU-MIMO configuration focusing on the dependency of the location of the MSs in Yokosuka, Japan. The majority of the measurement course is under line-of-sight (LOS) conditions in a single cell environment. The MSs are almost uniformly set 30 to 60 degrees in azimuth and 12 to 30 degrees in elevation and the distance from the BS antennas is approximately 150m at maximum. We also evaluate the performance of 4-by-2 MU-MIMO using the conventional type of horizontal array antenna and show the difference. The field experimental results show that throughput of greater than 1Gbps is achieved at the Cumulative Distribution Function (CDF) of 14% by employing SV-MIMO for Rank-4 MU-MIMO. The throughput of SV-MIMO is 30% higher than that for the horizontal array antenna configuration at the CDF of 50%.