在本篇論文中，我們針對大規模多輸入多輸出非正交多重接取下行系統發展干擾消除技術；此系統包含兩個基地台與多個使用者，其中每個基地台服務2K個使用者，且每兩個使用者構成一個群組。由於每個基地台將擬傳給K個群組之2K個使用者的訊號適當疊加與組合後再傳送出去，所以當兩個基地台同時傳送資料時，會產生群組干擾和基地台干擾。我們設計兩種預編碼器以克服這些干擾，其中第一種預編碼器消除群組干擾，而第二種預編碼器則消除基地台干擾；利用此兩種預編碼器，我們可將每一基地台內對應之雙基地台環境下的多群組多輸入多輸出非正交多重接取通道分解為多個獨立單群組多輸入多輸出非正交多重接取通道。另外，我們考慮單一群組內部的兩個使用者的資料偵測，並配合聯合功率分配、預編碼器和解碼器的設計，以改善系統的位元錯誤率。模擬結果顯示，我們所提出的預編碼器和解碼器在雙基地台環境下具有良好的位元錯誤率效能。

In this thesis, we investigate downlink massive multiple-input multiple-output (MIMO) non-orthogonal multiple access (NOMA) systems under a two-cell environment, where each cell consists of a base station and a number of users divided into multiple clusters of two users each. For this system, both intra-cell interference and inter-cell interference occur, and we propose two precoders to overcome the associated problems. One precoder is designed based on block diagonalization to eliminate the intra-cell interference, while the other precoder along with a zero-forcing matrix is designed based on interference alignment to remove the inter-cell interference. With such precoders and zero-forcing matrices, the corresponding multi-cluster MIMO-NOMA channel within each cell can be decomposed into multiple independent single-cluster MIMO-NOMA channels. Considering data detection for the two users in a single cluster, we also develop a joint power allocation, precoding, and decoding scheme to improve the bit error rate (BER) performance of the system. Simulation results demonstrate that the proposed scheme achieves excellent BER performance for downlink NOMA transmission in a two-cell environment.

Abstract i
Contents ii
List of Figures iii
I. Introduction 1
II. System Model 5
III. Proposed Methods 10
A. Intra-cell Interference Cancellation 10
B. Inter-cell Interference Cancellation 11
C. Optimal Decoder Design 15
D. Joint Power Allocation, Precoding, and Decoding 17
IV. Simulation Results 19
V. Conclusion 27
References 28

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