在本論文中，我們提出一種在可重構智慧表面(reconfigurable intelligent surface; RIS)輔助下之下行多輸入單輸出(MISO)非正交多重接取(non-orthogonal multiple access; NOMA)系統的聯合功率分配與預編碼技術；此系統包含多個使用者，並分成多個群組；每一群組由一個靠近基地台的使用者和一個遠離基地台的使用者組成，其中後者透過RIS的協助以接收來自基地台的訊號。本論文的目標乃藉由聯合最佳化基地台的預編碼向量、RIS的反射係數向量以及每個群組內的使用者功率分配因子，以便在一定的傳輸速率要求下最小化基地台的傳輸功率。我們首先利用區塊對角化技術開發多群組MISO-NOMA 通道對應的空間相關矩陣，以推導出可消除群組間干擾的預編碼器；這些預編碼器可將多群組通道轉換為多個平行的單群組通道，從而將一個多群組功率最小化問題簡化成多個相同的單群組功率最小化問題。針對每一單群組問題，我們進一步提出一個迭代式演算法以求得次佳解，其中對應的預編碼向量、RIS反射係數向量以及使用者的功率分配因子皆會在每次迭代過程中適當更新。電腦模擬結果顯示，與現有相關作法比較，我們針對RIS輔助MISO-NOMA系統所提出之聯合功率分配與預編碼技術可在一定的傳輸速率要求下有效降低基地台的傳輸功率。

In this thesis, we propose a joint power allocation and precoding scheme for a downlink multi-cluster multiple-input-single-output (MISO) non-orthogonal multiple access (NOMA) system with the assistance of a reconfigurable intelligent surface (RIS). In the system, the users are divided into multiple clusters; each cluster has one near user and one cell-edge user, where the cell-edge user receives assistance from the RIS. Our target is to minimize the total transmit power subject to a transmission rate requirement by jointly optimizing the precoding vector at the base station, the reflection coefficient vector at the RIS, and the users’ power allocation factor for each cluster. First, we derive some precoders based on block diagonalization (BD) that exploit spatial correlation matrices of the multi-cluster MISO-NOMA channel to eliminate inter-cluster interference. With these BD-based precoder, the multi-cluster channel is converted into multiple parallel single-cluster channels, and thus the multi-cluster power minimization problem can be simplified as several identical single-cluster power minimization problems. For each single-cluster case, we subsequently propose an iterative algorithm to obtain a suboptimal solution to the optimization problem, where the corresponding precoding vector, the reflection coefficient vector, and the users’ power allocation factor are updated properly at each iteration. It is demonstrated by computer simulation results that the proposed joint power allocation and precoding scheme for an RIS-assisted MISO-NOMA system can effectively reduce the transmit power under a transmission rate requirement, as compared with a previous related design.

Abstract
Contents
List of Figures
List of Tables
I. Introduction---------------------------------------------1
II. System Model---------------------------------------------4
III. Proposed Methods-----------------------------------------9
A. Inter-cluster Interference Cancellation------------------9
B. Optimization of the Precoding Vector--------------------11
C. Optimization of the Reflection Coefficient Vector-------13
D. Optimization of the Power Allocation Factor-------------14
E. Iterative Design of Power Allocation and Precoding------16
F. Complexity Analysis of the Iterative Design-------------17
IV. Simulation Results--------------------------------------19
V. Conclusion----------------------------------------------25
References----------------------------------------------------26

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