隨著科技的蓬勃發展，未來對於無線通訊系統的容量需求也日漸嚴苛，因為如此，非正交多重接取 (non-orthogonal multiple access；簡稱NOMA) 成為5G候選技術，並且開始受到重視。然而，使用者之間的干擾在NOMA系統下也是一個必須解決的難題。在論文中，基於NOMA系統的基本架構，我們進一步結合大規模多輸入多輸出 (massive multiple-input multiple-output；簡稱massive MIMO) 系統來提升整體的容量，提出了大規模多輸入多輸出非正交多重接取　(massive MIMO-NOMA) 下行系統。在此系統中我們首先考慮一個基地台 (base station；簡稱BS) 及多個使用者，此多個使用者會被兩兩分成多個群組。基地台會將給多個群組中的使用者們的訊號疊加後再廣播出去，因此群組干擾必然會產生。首先，各個群組會有各自的傳送端天線相關性的特徵向量，將群組干擾項各自的特徵向量做列擺放，形成一個大矩陣，並對其找出零核空間，透過干擾項的零和空間作為預編碼器的設計，可以將群組間的干擾消除。接著，考量到單一個群組兩個使用者解訊號的所有過程，我們提出最小化最大的均方誤差來設計同群組間使用者的功率分配演算法。為了更近一步改善使用者錯誤率的效能，得到群組組間的功率分配後，我們提出聯合功率分配、預編碼器和解碼器的設計，基於最小化所有使用者解自己訊號的均方誤差的總和，隨後我們推導出相對應的預編碼器和解碼器，並透過迭代演算法來將功率分配係數、預編碼器和解碼器交替最佳化，並達到收斂來得到最佳的功率分配、預編碼器和解碼器，用以改善系統的錯誤率。

In this thesis, we present a joint design for power allocation, precoding, and decoding in downlink massive multiple-input multiple-output (MIMO) non-orthogonal multiple access (NOMA) systems with a base station and multiple users, where the users are divided into multiple clusters of two users each. A precoder design based on block diagonalization (BD) is first proposed to eliminate the inter-cluster interference. With this, the multi-cluster MIMO-NOMA channel can be decomposed into multiple parallel independent single-cluster MIMO-NOMA channels. Considering all the decoding processes of the two users in a single cluster, we then derive a closed-form power allocation formula based on minimizing the maximum mean-squared error (MSE) of the corresponding decoded signals. Furthermore, we formulate an optimization problem in terms of the precoders and decoders for minimizing the sum of MSEs of all the users in the downlink massive MIMO-NOMA system under a total power constraint. A joint algorithm is subsequently developed to iteratively obtain the power allocation factors, precoders, and decoders until convergence. Simulation results demonstrate that the proposed joint design method provides a significant improvement in the bit-error-rate performance over the scheme using fixed power allocation, BD based precoding, and minimum MSE based decoding.

Contents
Absrtract 　 i
Contents 　 ii
List of Figures iii
I. Introduction.....................................................1
II. System Model.....................................................5
III. Propsoed Tranceiver Design.......................................8
A. Inter-cluster Interference Cancellation..........................8
B. Optimal Decoder Design..........................................10
C. Power Allocation Between the Two Users for a Single Cluster.....11
D. Joint Power Allocation, Precoding, and Decoding.................15
IV. Simulation Results..............................................18
V. Conclusion......................................................24
Appendix................................................................25
References..............................................................27

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