Downlink Path-Based Precoding Space-Time Block Code in FDD Massive MIMO Systems Without CSI Feedback

對於頻分多工大規模多輸出多輸入系統而言，因為需要大量的導航訊號以及回傳時間，下行訓練被視為一個不實際的方法。雖然有一些文獻提供了如何減少下性訓練及回傳時間的方法，但是減少的程度是有極限的。最近，部分文獻發現上行通道及下行通道的相似性，而基地台可以經由之前的上行通道測量來得到部分的通道資訊。藉由上行通道及下行通道資訊的相似性，有一些不需要下行訓練及通道資訊回傳的預編碼的方法被提出。在本篇論文中，我們提出了一個利用多路徑通道的多樣性且不需要通道資訊回傳的下行預編碼方法。更準確的說，我們利用部分通道資訊並應用空間時間區塊碼來加強下行傳輸的可靠性。實驗結果顯示，我們提出的方法只需要部分通道資訊且可以達到令人滿意的表現。For a massive multiple-input-multiple-output (MIMO) system operated under frequency-division duplex (FDD), downlink training was usually considered impractical due to huge amount of pilot signals and feedback overhead. Although some efforts have been spent to reduce such an overhead in recent works, the reduction is still limited. More recently, some precoding methods that do not require downlink training and channel state information (CSI) feedback have been proposed by recognizing some similarity between uplink and downlink channels. The base station may take advantage of such similarity and acquire partial knowledge of the downlink channels using previous uplink channel estimates. In this thesis, we propose to further exploit the diversity of a multipath channel in a downlink precoding method without CSI feedback. Specifically, space-time block code (STBC) is applied to enhance the robustness of downlink transmission based on the partial CSI at the transmitter (CSI-T). Simulation results suggest that the proposed method achieves a competitive performance to other methods with only the partial CSI-T