在多使用者中之頻率分工巨量多天線系統下使用部分 通道資訊之混合式波束成型設計

Abstract

在此論文中, 我們為頻率分工 (Frequency Division Duplex) 下巨量天 線 (Massive MIMO) 系統構想了一個有效的部分通道資訊 (Partial CSIT) 回授方式, 基於此方式, 我們提出了波束成型 (Beamforming) 的設計訪 法。部分通道資訊在本論文中的形式為下行 (Downlink) 傳輸時的訊號 路徑發射角度以及各路徑上的增益。利用下行傳輸發射角度與上行 (Uplink) 傳輸訊號接收角度之間的互惠性 (Reciprocity), 部分通道資訊 可經由下行訓練以及上行回授有效取得。因此, 巨量天線系統的可行性 大幅增加。然而在毫米波 (mmWave) 通訊中,由於射頻電路的高成本 和高功率的耗損,因此在波束成型技術方面上,不只提出了傳統上全 數位的波束成型,以及混合式的波束成型。模擬結果顯示了我們所提 出的方法之優越性,除此之外,在混合式波束成型方面,我們所提出 的方法只需要少數的射頻電路,即可達到與全數位的波束成型技術有 同樣的效能。

In this thesis, we consider an effective acquisition mechanism of partial channel state information at the transmitter (CSIT) for frequency-division du- plex (FDD) massive MIMO systems, based on this phenomenon, we propose downlink beamforming methods. The partial CSIT is in the form of down- link angles of departure (AoDs) and the amplitudes of the strongest paths of each UE. By exploiting the reciprocity between downlink AoDs and uplink angles of arrival (AoAs), the partial CSIT can be acquired through down- link training and uplink feedback effectively. Therefore, the feasibility of FDD massive MIMO systems is greatly enhanced. However, in millimeter wave (mmWave) communication, due to the high cost and power consump- tion of high-bandwidth RF chains. Thus, in beamforming proposed methods, we not only propose the conventional fully-digital beamforming but also hy- brid beamforming. The proposed beamforming methods enable the BS to perform DL transmissions to multiple UEs simultaneously. Simulation re- sults demonstrate the superiority of the proposed methods compared to other methods in the sense of fairness and achievable sum rate in conventional fully- digital beamforming. In addition, in hybrid beamforming, we only use a few of RF chains that the proposed method can realize the conventional fully- digital beamforming.