在此博士論文中，我們研究在多重輸入多重輸出(Multiple-Input Multiple-Output, MIMO)正交分頻多工(Orthogonal Frequency-Division Multiplexing, OFDM)系統上基於室內毫米波通道(Millimeter Wave, mmWave)的混合式波束形成(Hybrid Beamforming)設計。在考慮混合式波束形成於多載波系統 (Multi-Carrier System)的實際硬體限制之下，我們提出子系統奇異值分解 (Sub-System SVD)混合式波束形成演算法。此方法不但擁有良好的系統效能，也具備較低的運算複雜度。為了進一步減少通道估計(Channel Estimation)的系統複雜度，在此論文中我們也討論如何降低波束形成演算法所需要的通道狀態訊息(Channel State Information, CSI)總量。基於室內毫米波通道的統計特性，我們有效降低子系統奇異值分解演算法所需求的通道狀態訊息量。此外，我們也將子系統奇異值分解演算法延伸至有限回饋(Limited Feedback)的系統架構上。在考量有限回饋的系統中，接收端只能回饋有限的訊息給傳送端，因此傳送端只能根據有限的訊息回饋進行波束成形設計。基於有限回饋的架構， 我們提出有限回饋子系統奇異值分解(Limited Feedback Sub-System SVD, LSS) 演算法。此演算法包含三個部分:第一個部分是由化簡子系統奇異值分解演算 法所產生的類比預編碼器(Analog Precoder)編碼簿(Codebook)設計、第二個部分是由羅依類型(Lloyd-Type)演算法所獲得的數位預編碼器(Digital Precoder)編碼簿設計、第三個部分則是大幅提升碼字(Codeword)搜尋速度的低複雜度碼字篩選演算法。最後，我們討論子系統奇異值分解演算法與有限回饋子系統奇異值分解演算法在現實系統缺陷中的穩健性。我們考量的現實系統缺陷包含三種效應:量化的類比波束形成器(Beamformer)、有瑕疵的通道狀態訊息、和低解析度(Low-Resolution)類比數位轉換器(Analog-to-Digital Converter)。藉由電腦模擬，我們發現子系統奇異值分解演算法不但趨近傳統全數位(Full-Digital)波束形成演算法的效能，還具備了低運算複雜度。在有限回饋的系統中，有限回饋子系統奇異值分解演算法則提供了比以往的演算法 更好的系統效能。此外，當通道狀態訊息總量被大幅降低時，我們所提出的演 算法都保有不錯的系統效能。在現實系統缺陷效應下，我們所提出的演算法也都維持很好的表現，且在較低的量化位元(Quantization Bit)下就可以達到飽和的系統效能。

In this dissertation, the hybrid beamforming design for multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems is studied over the indoor millimeter wave (mmWave) channels. Under practical hybrid beamforming constraints for multi-carrier systems and the study of sub-systems, we propose the sub-system SVD (SS) hybrid beamforming design which provides good performance with low complexity. To alleviate the complexity problem of channel estimation, reduction of the amount of required channel state information (CSI) is also studied based on the statistical properties of indoor mmWave channels. The SS hybrid beamforming algorithm is then extended to the limited feedback scheme in which the transmit beamformers are designed based on limited information fed back from the receiver. The limited feedback sub-system SVD (LSS) algorithm is proposed, which includes three parts: the simplified SS algorithm for the the analog precoder codebook design, the Lloyd-type algorithm for the digital precoder codebook design, and a low-complexity codeword selection algorithm to reduce the search complexity. The impact of imperfect system effects, including the quantized analog beamformer, imperfect CSI, and low-resolution analog-to-digital converter, is also examined. Simulation results show that our SS algorithm achieves the performance level of traditional full-digital beamforming with low complexity and the LSS algorithm has good performance even if the amount of CSI is greatly reduced. Under imperfect system effects, we also demonstrate that the proposed algorithms maintain good results and require less quantization bits to achieve saturated performance.

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