Implementation and Evaluation of Real-Time Distributed Zero-Forcing Beamforming for Downlink Multi-User MIMO Systems

Tomoki MURAKAMI  Koichi ISHIHARA  Riichi KUDO  Yusuke ASAI  Takeo ICHIKAWA  Masato MIZOGUCHI  

IEICE TRANSACTIONS on Communications   Vol.E96-B    No.10    pp.2521-2529
Publication Date: 2013/10/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.E96.B.2521
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Recent Progress in Antennas and Propagation in Conjunction with Main Topics of ISAP2012)
Category: Wireless Communication Technologies
multiuser MIMO,  inter-cell interference,  distributed system,  wireless LAN system,  

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The implementation and experimental evaluations of distributed zero-forcing beamforming (DZFBF) for downlink multi-user multiple-input multiple-output (DL MU-MIMO) systems are presented. In DZFBF, multiple access points (APs) transmit to own desired stations (STAs) at the same time and using the same frequency channel while mitigating inter-cell interference. To clarify the performance and feasibility of DZFBF, we develop a real-time transmission testbed that includes two APs and four STAs; all are implemented using field programmable gate array. For real-time transmission, we also implement a simple weight generation process based on ZF weight using channel state information which is fed back from STAs; it is an extension of the weight generation approach used in DL MU-MIMO systems. By using our testbed, we demonstrate the real-time transmission performance in actual indoor multi-cell environments. These results indicate that DL DZFBF is more effective than DL MU-MIMO with time division multiple access.