在合作式網路通訊系統之中，不論是在多個中繼站中選擇最佳的一個來幫助傳送端傳送訊號、或是中繼站選擇是否幫助傳送端傳送訊號，現有的文獻所探討的系統，都是根據瞬間通道狀況來做判斷，但是這樣的方法會有很高的複雜度，尤其當通道劇烈改變時，系統沒有足夠的時間作出決定。
我們在此研究中提出了利用通道統計特性選擇直接傳送 (Direct Transmission,DT) 、放大後傳送(Amplify-and-Forward, AF) 或是解碼後傳送(Decode-and-Forward, DF) 的方式。在本論文之中，系統的效能分析是依據通道的平均容量，而不論中繼站使用放大後傳送(AF)還是解碼後傳送(DF)，我們都利用了幾個不同的不等式化簡通道容量平均的理論值，並且求得選擇合作的門檻。
本論文也藉由電腦模擬來驗證理論推導的結果，由模擬圖分析可知使用合作門檻的傳送方式可以有效的選擇甚麼時候該使用合作式通訊。

In cooperative communications systems, multiple relays selection scheme and adaptive relay selection scheme are usually adopted. In both schemes, the system makes selections based on instantaneous channel status. However, such schemes have an extremely high computational complexity. In particular, when the channels experience fast fading, the systems do not have sufficient to make a correct decision.

In this thesis, statistical channel properties are utilized in deciding whether cooperative transmission should be adopted or not. In our investigations, the cooperative mechanism includes direct transmission (DT), decode-and-forward (DF) relaying and amplify-and-forward (AF) relaying. The Ergodic capacity is adopted throughout the theoretical analyses. In addition, a number of approximated thresholds are derived to assist the decision process.

Simulation experiments are conducted to verify the derived results. It is shown that the proposed transmission scheme using the cooperative thresholds is effective in deciding when the cooperative communication is necessary.

致謝…….................................................................................................................................... I
中文摘要.. ................................................................................................................................ II
Abstract…. .............................................................................................................................. III
Chapter 1 Introduction ............................................................................................................. 1
1.1 Introduction of Cooperative Network ......................................................................... 1
1.2 Introduction of Cooperative Transmission Protocols ................................................... 2
1.3 Literature Review.......................................................................................................... 3
Chapter 2 System Model ........................................................................................................ 10
2.1 Direct Transmission System ....................................................................................... 10
2.2 Conventional Single-Relay Cooperative System ........................................................ 11
2.2-1 Ergodic Capacity of Decode-and-Forward Relaying ..................................... 13
2.2-2 Ergodic Capacity of Amplify-and-Forward Relaying .................................... 16
Chapter 3 Approximate Threshold Functions for Selective Cooperation ......................... 19
3.1 Decode-and-Forward Relaying and Direct Transmission ........................................... 19
3.1-1 Approximation of Exponential Integral .......................................................... 19
3.1-2 Approximation by Jensen’s Inequality ........................................................... 21
3.2 Amplify-and-Forward Relaying and Direct Transmission ......................................... 22
3.2-1 Approximation of Exponential Integral .......................................................... 22
3.2-2 Approximation of Jensen’s Inequality ............................................................ 23
3.3 Hybrid Cooperative Protocol and Direct Transmission .............................................. 26
Chapter 4 Simulation Results ................................................................................................ 27
Chapter 5 Conclusions and Future Works ........................................................................... 40
5.1 Conclusions ................................................................................................................. 40
5.2 Future Works .............................................................................................................. 40
References ............................................................................................................................... 41
Abbreviations .......................................................................................................................... 45

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