チャネル状態情報が一部欠損したときの部分的非直交ブロック対角化に基づく基地局間連携マルチユーザMIMO伝送法

摘要

We consider a precoding method in downlink multiuser multiple-input multiple-output (MIMO) transmission with the multiple base station (BS) cooperation, where some of the instantaneous channel state information (CSI) is not available at the BS. The proposed precoding scheme is based on the block diagonalization of the channel matrix. However, since some elements of the channel matrix are unknown, we allow a partially non-orthogonal transmission. More specifically, we allow the inter-user interference to the users with limited instantaneous CSI feedback from the channel where instantaneous CSI of that user is not obtained at the BS. The other inter-user interferences are set to zero based on the block diagonalization of the channel matrix. The proposed method can efficiently use the degree of the freedom of the spatial channel compared to the case with full orthogonal transmission at the cost of increased inter-user interference to the users with limited instantaneous CSI feedback. Simulation results elucidate that the proposed method can increase the capacity for a given transmission power or decrease the transmission power for a given capacity requirement compared to the case with full orthogonal transmission.%本稿では，下りリンク基地局(BS：base station）間連携マルチユーザMIMO（multi-input multi-output）において，一部の受信端末（MS：mobile station）のMIMOチャネル状態情報（CSI：channel state information）が不明な場合の伝送法を検討する．CSIに基づくプリコーディング法として，空間多重するMS間の干渉をヌリングするブロック対角化法をべースとする部分的非直交型ブロック対角化法を提案する．提案法はCSIの一部が不明なMS間の干渉を許容し，その他のMS間の干渉はブロック対角化を用いてヌリングすることでMIMOチャネルの自由度を増大させる．シミュレーション結呆から，提案法はMIMOチャネルの自由度をより活用できるため，完全直交性を確保する場合に比較してシステム性能を改善できることを示す．