本篇論文探討多基地台環境下之大規模MIMO合作式非正交多重接取下行系統的干擾消除技術，每個細胞中有多個群組，每個群組中有二個使用者，並以合作式策略對資料做偵測。為了降低系統中細胞間干擾以及群組間干擾，我們首先提出基於干擾通道校準以及對角化技術之預編碼方式。透過干擾通道校準以及對角化技術之預編碼方式，可以將多重細胞多重群組MIMO非正交多重接取下行系統分解為多個獨立單一細胞且多個平行單一群組的MIMO非正交多重接取下行系統。接著，我們提出了功率分配、預編碼與解碼之聯合設計，以提高單一群組的偵測性能。再單一細胞中，對於單一群組兩個合作式非正交多重接取下行系統之使用者來說，根據最大化最小之接收訊雜比標準來決定功率分配參數。而用戶的解碼器是基於最小化均方誤差（MSE）而設計的，並且利用最小化細胞中所有用戶MSE的總和來導出相對應的預編碼器。利用迭代的方式對所有功率分配參數、預編碼器和解碼器更新直到收斂。模擬結果顯示，我們所提出的大規模MIMO合作式非正交多重接取下行系統之多基地台環境可以達到優異的位元錯誤率效能，而其表現優於既有的基於干擾通道校準之預編碼技術。

In this thesis, we investigate a downlink massive multiple-input multiple-output (MIMO) cooperative non-orthogonal multiple access (NOMA) system under multicell environments, where each cell includes multiple clusters and each cluster contains two users with a cooperative strategy for data detection. To reduce both intercell interference and intercluster interference in such systems, we first propose a precoding scheme based on interference channel alignment (ICA) and block diagonalization (BD) techniques. With ICA-BD precoding, a multicell multi-cluster MIMO-NOMA channel can be decomposed into multiple independent single-cell parallel single-cluster MIMO-NOMA channels. Then, we propose a joint design for power allocation, precoding, and decoding to improve the detection performance in a single cluster. For a cluster of two cooperative NOMA users in a cell, power allocation factors are determined according to the maximum minimum received signal-to-noise ratio criterion. The users’ decoders are designed based on minimizing the mean-squared error (MSE), and the corresponding precoders are derived by minimizing the sum of MSEs of all users in the cell. All of the power allocation factors, precoders, and decoders are updated iteratively until convergence. Simulation results show that the proposed scheme achieves excellent bit-error-rate performance for downlink cooperative NOMA transmission under multicell environments, which is much better than that of an existing ICA-based scheme.

I. Introduction 1
II. Multicell Massive-MIMO Cooperative NOMA Downlink System 6
A. Channel Model 7
B. System Model 8
C. Multicell Environments 10
D. Relaying Phase 11
III. Proposed ICA-BD Method for Multicell Environments 12
A. Intercell Interference Cancellation 12
B. Intercluster Interference Cancellation 16
IV. Proposed Power Allocation and Detection for Single-Cell Environments 18
A. Optimal Power Allocation 18
B. NOMA Phase - Optimal Decoder Design 22
C. NOMA Phase - Joint Power Allocation, Precoding, and Decoding 23
D. Relaying Phase – Optimal Decoder Design and MRC 24
V. Simulation Results 26
VI. Conclusions 34

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