在本論文中，我們針對包含兩個使用者的點陣劃分下行非正交多重接取系統提出改良式調變方法；在現有的系統中，傳送端根據通道增益的大小決定強使用者和弱使用者，並將弱使用者的訊號和強使用者的訊號分別調變在較高的位元層級和較低的位元層級傳送，這意謂前者的傳送功率大於後者的傳送功率。相較之下，我們所提出之方法乃將每一使用者訊號分成高低兩個位元部分，而結合強弱兩個使用者的訊號則包含四個位元部分，依序稱為第一 (最高) 、第二、第三、第四位元部分；為符合非正交多重接取原理，弱使用者訊號的高位元部分一律被調變在第一位元部分傳送，而強使用者訊號的高位元部分則一律被調變在第二位元部分傳送；至於強弱二使用者的低位元部分則可分別被調變在第三、四位元部分或第四、三位元部分傳送。理論分析和電腦模擬結果顯示，我們所提出之改良式調變方法比現有作法具有較高的系統容量。

In this thesis, we propose improved modulation schemes for a two-user lattice-partition-based (LP-based) downlink non-orthogonal multiple access (NOMA) system. In existing two-user LP-based NOMA systems, the transmitter identifies one user with a larger channel gain as the strong user and another user with a smaller channel gain as the weak user. Then it modulates the weak user’s signal at more significant bit (MSB) levels and the strong user’s signal at less significant bit (LSB) levels for NOMA transmission, where more power is allocated to the former than to the latter. For the proposed modulation schemes, each of the users’ signal is split into MSBs and LSBs, and the combined strong and weak users’ signal for NOMA transmission consists of four parts of bits, referred to as Parts I, II, III, and IV according to the order of levels. To meet the NOMA principle, the MSBs of the weak user and those of the strong user are always modulated at Parts I and II, respectively, for transmission. On the other hand, the strong user’s LSBs and the weak user’s LSBs can be modulated at Parts III and IV, respectively, or at Parts IV and III, respectively. Both theoretical analysis and computer simulation results are given to verify that the proposed modulation schemes offer higher system capacity than the existing method for two-user LP-based NOMA systems.

Abstract
Contents
List of Figures
I. Introduction------------------------------------1
II. Background--------------------------------------3
A. A Downlink NOMA Model---------------------------3
B. Fundamentals of LPMA----------------------------4
C. The Deterministic Model for Downlink NOMA-------5
D. A Downlink LPMA Model---------------------------5
III. Improved Modulation Schemes---------------------7
A. Proposed Methods--------------------------------7
B. Capacity Analyses-------------------------------8
IV. Simulation Results-----------------------------10
V. Conclusion-------------------------------------13
References---------------------------------------------14

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