Survey of Transmission Methods and Efficiency Using MIMO Technologies for Wireless LAN Systems


IEICE TRANSACTIONS on Communications   Vol.E98-B    No.7    pp.1250-1267
Publication Date: 2015/07/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.E98.B.1250
Type of Manuscript: INVITED SURVEY PAPER
MIMO,  MU-MIMO,  transmission efficiency,  overhead,  access control,  MAC protocol,  CSI feedback,  implicit beamforming,  PHY,  

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Multiple-input multiple-output (MIMO) transmission is attracting interest for increasing the transmission rates of wireless systems. This paper surveys MIMO transmission technology from the viewpoints of transmission methods, access control schemes, and total transmission efficiency. We consider wireless local area networks (WLAN) systems that use MIMO technology; moreover, we focus on multiuser MIMO (MU-MIMO) technology, which will be introduced in next-generation WLAN systems such as IEEE802.11ac. This paper explains the differences in the detailed access control procedures for MIMO and MU-MIMO transmission, including channel state information (CSI) acquisition. Furthermore, the issues related to CSI feedback and solutions are also discussed. Related works on the medium access control (MAC) protocol in MIMO/MU-MIMO transmission are introduced. In addition, the throughput performance using MIMO/MU-MIMO transmission is evaluated considering an IEEE802.11ac-based WLAN system. From the numerical evaluation, it is shown that the overhead due to CSI feedback from the user terminals to the base station causes a decrease in the throughput. We verified that implicit beamforming, which eliminates CSI feedback, is effective for solving this issue.