在毫米波 (Millimeter Wave, mmWave) 多輸入多輸出 (multiple-input multiple-output, MIMO) 通訊系統中，傳統的全數位波束成形 (Full-Digital Beamforming) 需配置大量的射頻鏈 (Radio Frequency Chain, RF Chain)，造成硬體複雜度過高和能量消耗過多等問題。因此結合了數位波束成形和類比波束成形的混和式波束成形 (Hybrid Beamforming) 架構被考慮應用在毫米波頻段通訊，來解決硬體限制問題。
本論文探討在IEEE 802.15.3c毫米波通道模型下，多用戶多載波系統的混合式波束成形設計，我們提出了非迭代式的混合式波束成形演算法，藉由子系統奇異值分解 (Sub-System Singular Value Decomposition, Sub-System SVD) 找到增益較強的等效通道，而在基頻 (Baseband) 使用區塊對角化 (Block Diagonalization, BD) 預編碼 (Precoding) 來消除使用者之間的干擾。透過模擬，我們比較不同演算法在直視性 (Line-of-Sight, LOS) 和非直視性 (Non-Line-of-Sight, NLOS) 之室內毫米波通道環境下的效能。
IEEE 802.15.3c通道模型描述了毫米波通道的時間及空間統計特性，藉由分析通道模型的統計特性，我們可以簡化設計方法，進一步降低運算複雜度，同時效能仍維持與原本演算法相同的水準。從模擬結果可知當系統參數改變，我們的演算法於高訊雜比 (Signal-to-Noise Ratios, SNRs) 下仍能有接近全數位區塊對角化方法的效能，且大幅降低所需的射頻鏈數量。

Hybrid beamforming that combines digital beamforming and analog beamforming is widely considered to be employed to reduce the necessary hardware in massive multiple-input multiple-output (MIMO) systems and overcome the strong path loss at millimeter wave (mmWave) frequencies. This study aims to develop hybrid beamforming design for downlink multi-user multi-carrier MIMO systems. On the basis of the sub-system singular value decomposition to enhance the signals for designing analog beamformers and digital combiners, and block diagonalization (BD) scheme to eliminate inter-user interference for designing
digital precoders, we propose a non-iterative hybrid beamforming algorithm.
The IEEE 802.15.3c channel model which captures the statistical properties of temporal and spatial domains of the indoor mmWave channel is adopted in this study. We also investigate channel statistical behavior to develop an algorithm that can achieve low computational complexity without obvious performance degradation. Simulation results indicated that the proposed algorithm with reasonable amount of transmit RF chains approaches the performance of the asymptotically optimal full-digital BD algorithm at high signal-to-noise ratios.

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