在下世代行動通訊系統中，為了提高資料傳輸速率 ，巨量多輸入多輸出系統在這幾年已經成為熱門研究的主題。在此系統中，我們可以藉由打出較窄的波束，讓訊號在想要的方向有較高的功率增益。因為天線數的大幅增加，訊號的最佳發射方向需要耗費大量時間才能找到，讓時間複雜度提升許多。因此，為了降低搜尋時間，多解析度波束成型訓練的方法就被提出來解決這個問題。為了使用多解析度波束成型訓練的方法，階層式編碼簿需要提前被設計出來。在我的研究中，多解析度波束成形的設計主要可以分成兩種類型。第一種是先把多個彼此正交的波束結合起來後，再擷取其相位當作我的編碼簿。因為把多個波束結合起來，其中就有波束之間的相對相位需要設計，我們藉由高解析度的相位搜尋，找到最佳的相對相位，使設計完的波束在特定的範圍有更好的功率增益。第二種方法是降低相對相位搜尋複雜度的方法。我們發現如果把兩個正交波束結合，只需要從少數幾個區間去取樣出相對相位，就可以把所有不同的波束找到。我們把這個發現延伸到多個正交波束結合的情況，如此一來相位的搜尋複雜度就大幅降低。最後藉由波束對漏損量的比值以及波束功率的變異數來評斷設計出來的波束的優劣好壞，最後模擬結果也證實了這個方法改善了傳統的作法。

To increase the data transmission rate in the next generation mobile communication system, massive multiple-input multiple-output(MIMO) systems has become a hot research for the past few years. In this system, we can transmit a narrow beam to make a higher power gain in the desired range. But due to a large number of antennas at both TX/RX sides, the optimal beam direction need to be search for a long time and thus make a higher time complexity. In order to decrease the search time, the multi-resolution beamforming training is proposed to solve this problem. In order to use the multi-resolution beam training method, a hierarchical codebook need to be design in advance. In the hierarchical codebook design, we first proposed to combine multiple orthogonal beams, and extract the phase of combined beam as the codebook. In this method, the relative phase of beams need to be search. By using the high resolution relative phase search, the optimal beamforming pattern can be found. In order to reduce the search of relative phase of beams, a beam by beam combined method is proposed. We find that if we combine two beams and then extract the phase of combined beam, all beamforming pattern can be found by sampling the relative phase in the several intervals and this can be extended to multiple beam combined case. We evaluate our codebook design by using the beam to leakage ratio (BLR) and variance. The simulation results show that our method indeed improves the traditional method.

ABSTRACT II
誌謝 IV
CONTENTS V
LIST OF FIGURES VI
LIST OF TABLES IX
Chapter 1 Introduction 1
1.1 General Background Information 1
1.2 Related Works 3
Chapter 2 System Model and Channel Model 5
2.1 Hybrid Precoding for Massive MIMO System 5
2.2 Channel Model 6
2.3 Problem Formulation 8
Chapter 3 Multi-Resolution Beamforming Training 10
3.1 The Sequential Search Scheme 10
3.2 The Hierarchical Multi-Resolution Beamforming Training 11
Chapter 4 Hierarchical Codebook Design 15
4.1 Codebook Structure 15
4.2 Existing Hierarchical Codebook Design 17
4.3 Proposed Hierarchical Codebook Design 21
4.4 Codebook Construction Algorithm 31
Chapter 5 Simulation Results 38
5.1 Theoretical Analysis of Beamforming Training 38
5.2 Performance for Proposed Hierarchical Codebook Design 39
Chapter 6 Conclusion 57
References 58
APPENDIX A 61
APPENDIX B 63

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