為了符合第五代行動通訊服務大量高速傳輸的需求，非正交多工傳輸(Non- orthogonal multiple access, NOMA) 成為目前相當熱門的候選關鍵技術；這是由於NOMA系統能讓基地台以同一頻譜服務多個使用者，藉由傳輸能量差異及疊加編碼(Superposition coding)的使用，達成使用者的多工傳輸的效果，因此，此技術可以有效提高頻譜使用效率及系統總傳輸率，且對於蜂巢系統常見的對遠近效應(near-far effect)具有高抗性。然而，若基地台具備多天線，NOMA僅在使用者們與基地台之間的通道方向相近時，可達到較佳效果；反之，若使用者與基地台的通道方向夾角較大時，採用強制歸零(Zero-forcing, ZF)的預編碼設計，能更有效地降低使用者之間的訊號干擾。此篇論文將探討下行鍊路(Downlink)中，基地台分別以NOMA及ZF技術進行多工；在NOMA多工傳輸時，我們採用測地線幾何法(Geodesic geometry) 架構基地台傳送訊號的波束賦型向量，而接收端也採用連續干擾消除法(Successive interference cancellation, SIC)消除其他使用者的干擾訊號雜訊，基於通道資訊完美已知的假設下，我們提出讓總傳輸率達到最大值之最佳波束賦型向量及功率分配之設計，同時確保距離較遠之使用者之傳輸權益；同理，我們也針對ZF多工傳輸求得其最佳功率分配。然而，由於無線通道的衰變現象，通道增益值隨著時間變動，相較之下，若使用者與基地台之間的相對移動較慢，其與基地台之間之通道方位向量則較為穩定，因此，我們放寬了通道設定，假設基地台僅基於通道的方位向量及通道增益的統計特性，分別求得NOMA多工的最佳波束賦型向量及功率分配，及ZF多工的最佳功率分配，以減輕系統交換通道資訊所需的額外負擔。透過模擬結果，我們可以探討在各種通道狀況之下，是否該切換至NOMA或ZF多工模式，可得到較高之總傳輸率。

Due to dramatically increasing demand on high-speed wireless transmission, non-orthogonal multiple access (NOMA) becomes a popular candidate technology in in the fifth-generation mobile broadband standard because NOMA technology enables the base station (BS) to serve multiple users over the same spectrum. Through superposition coding, NOMA technology provides multiple access in power domain. Hence, it can effectively enhance spectrum efficiency and is robust to combat the near-far effect. However, NOMA achieves higher sum rate only when the geographical angles among the users are close to each other. By contract, adopting zero-forcing (ZF) transmission leads to higher sum rate when the geographical angles among the users are large. To explore more insight, we propose a joint optimization of beamforming vector and power allocation for the NOMA scheme and an optimal power allocation for ZF scheme respectively in order to maximize sum rate of the multiuser downlink and guarantee achievable rate of the weaker user. Specifically, we employ geodesic geometry method to obtain the optimal beamforming vector. We first optimize both schemes based on an ideal assumption of perfect channel state information (CSI). However, obtaining perfect CSI requires significant overhead. To relax the stringent requirement, we perform optimizations of both schemes under the scenario that the BS only has instantaneous channel direction information (CDI) and statistical channel gain information since channel gain varies more rapidly than channel direction under wireless fading channel. Through simulation results, we can easily find the switching point among the NOMA and ZF scheme in order to achibe the highest sum rate.

目錄
論文審定書 i
致謝 ii
摘要 iii
Abstract iv
圖目錄 vii
第一章 簡介 1
第二章 系統架構 5
第三章 完美通道下的波束賦形設計和功率分配 10
3.1 非正交多工存取系統 10
3.2 強制歸零系統 18
第四章 只有CDI情況下的波束賦形設計和功率分配 21
4.1 非正交多工存取系統 21
4.2 強制歸零系統 29
第五章 模擬結果 33
3.1 通道狀況完美已知 34
3.2 通道狀況部分已知( CDI ) 39
第六章 結論 46
參考文獻 47

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