本篇論文研究如何在兩次跳躍的環境下運用放大前向 (Amplify-and-Forward, AF) 的正交分頻多工 (Orthogonal Frequency Division Multiplexing, OFDM) 系統之中繼 (Relay) 端子載波功率分配研究。在此研究中假設訊號源 (Source) 端每一個子載波上的傳送功率為均勻功率分配 (Uniform Power Allocation)。
考慮系統運用分散式的總功率限制。意思為訊號源與中繼端各自限制其總傳送功率，兩者不相關。傳統的遞迴式充水式演算法 (Iterative Water-Filling Algorithm) 其目的雖可以達到最大的系統容量，然而，此演算法需要很高的運算複雜度；而且在訊號源端使用均勻功率分配下，系統容量的改善會被限制。在中繼端利用子載波功率分配來最大化系統容量實際上並不可行。
為了更提升系統的效能，我們藉由最小化在終點 (Destination) 端等效的雜訊功率，對於中繼端傳送訊號提出一種全新且有封閉解 (Closed-Form Solution) 的子載波功率分配方式。由分析與模擬結果可知與傳統功率分配方式比較，我們提出來的功率分配方式可以改善系統的平均位元錯誤率 (Average Bit Error Rate, ABER)。

This thesis studies the subcarrier power allocation for the relayed signal in Orthogonal Frequency-Division Multiplexing (OFDM) based dual-hop system where the relay node operated in amplify-and-forward (AF) scheme. The investigated system assumes that each subcarrier at the source node transmits the signal with uniform power distribution.
Considering the separated sum power constraints which the power constraint at source and relay node are uncorrelated, the conventional iterative water-filling algorithm can maximize the system capacity. However, it requires high computational complexity and the performance improvement is limited when the source node transmits the signal with uniform power distribution, subcarrier power allocation at relay node for capacity maximization is impractical.
To further enhance the system performance, a novel subcarrier power allocation method is derived into a closed-form for the relayed signal to minimize the summation of equivalent noise power of the destination node. Comparing with the existing schemes, simulation results demonstrate that the proposed power scaling scheme significantly improves system average bit error rate (ABER).

Chapter 1 Introduction………………………..……………………….......…1
1.1 Introduction of Relaying Network and Dual-hop System..……..………...............................................................….1
1.2 Introduction of OFDM………….…................……......…….2
1.3 Literature Review……………...………..………....……….2
1.4 Introduction of Proposed Power Allocation Method.......3
1.5 The Structure of Thesis……...........................................…5
Chapter 2 System Model…….......................................………..6
2.1 OFDM System Architecture………..............……….…..…6
2.2 OFDM-based Dual-hop in AF Relaying System Model.............................................................................................10
Chapter 3 Conventional Power Scaling and Subcarrier Power Allocation Schemes……..........................………….…15
3.1 APS and IPS……………..................................……….…..15
3.2 Optimal Power Allocation for AF OFDM Relaying….....16
Chapter 4 Proposed Power Scaling and Subcarrier Power Allocation Schemes…………………………………………………….….21
4.1. Problem fomulation....................................................................................21
4.2. Average Sum Power Constraint of Relay Node…........22
4.3. Instantaneous Sum Power Constraint of Relay Nod...24
Chapter 5 Simulation Results……………..............…………29
Chapter 6 Conclusions and Future Works…………............40
6.1. Conclusions…………………..………………………………..40
6.2. Future Works……………………...............…………………………….41
Abbreviations………………..………………………………….42
References……………...…………………………………..….45

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