Y型MIMOネットワーク符号化及び協力ヌルビームフォーミング

摘要

Infrastructure wireless mesh network has been attracted much of attention due to a wide range of its application such as public wireless access, sensor network, etc. The application of current MAC protocols to mesh network to support transmission of multiple unicast flows reveals inefficiency in resource (time and frequency) usage. In recent years, researchers show that significant network throughput gain can be achieved by employing network coding in a wireless environment. Also, for further improvement of network throughput in one dimensional (1-D) mesh topology, it is proposed to use multiple antenna technique combined with network coding. Being inspired by MIMO network coding in 1-D topology, in this paper, the authors establish a Y-typed MIMO network coding algorithm for a tree topology consisting of two branches. In this algorithm, network coded flows of branches are spatially multiplexed. Owing to the efficient sharing of frequency of network coding and co-channel interference cancellation ability of MIMO, the proposed algorithm shows an 8-fold gain in network capacity compared to conventional methods. Furthermore, by employing freedom of antenna used at each mesh node, the authors also propose a cooperative null beamforming algorithm suppressing interference when inter-route interference is taken into account. Finally, power control is combined with the proposed algorithms for best improvement of network capacity.%MIMOネットワーク符号化は双方向のマルチホップ中継を単一チャネルで高効率に実現する通信方式として注目を集めている．本稿では2次元化したY型MIMOネットワーク符号化をツリー型メッシュネットワークへの検討を行ったので報告する．Y型MIMOネットワーク符号化では，MIMOネットワーク符号化された複数のルートが合流し，ツリー型メッシュネットワークを構成する．提案法では合流ルートにおいて4素子以上のアンテナ素子を有したMIMOノードを配置することで単一チャネルによる高効率なツリー型双方向マルチホップネットワークを実現している．また合流点付近の中継ノードの余剰アンテナを用いてルート間および合流点への与・被干渉を回避する協力ヌルビームフォーミングや各中継ノードにおける信号対干渉雑音比（SINR）のバランスを考慮する電力制御も合わせて適用することで更なる効率の改善が可能となる.