在分組衰落通道下非正交合作式通訊網路的傳送方法

Abstract

在本篇論文中，我們考慮一種半雙工(half-duplex)的三個端點間合作式無線通訊系統，並且分析了在以時槽為單位的分組衰落 (block-fading) 通道環境下的兩種不同方法的合作式通訊 (Cooperative communication)。一種是放大前向 (Amplify-and-Forward) 的合作方法，另外一種是解碼前向 (Decode-and-Forward) 的合作方法。 我們將討論一種在合作式通訊網路非正交的傳送方法，它的定義是來源端會持續的在整個合作式的時間區段內傳送待傳的資料到終端。我們假設，每一個時槽單位是準靜態(quasi-static)的分組衰落通道環境，就是指通道的狀態在一個時槽會維持常數，但是在下一個時槽就會改變。在這種假設下，去重送我們要傳的資料。 這種新的傳送方法，在選擇性解碼前向以及放大前向的這兩種合作式方法下，都在比較低的系統數據速率下會有比較好的效能。從模擬的結果也發現，它跟傳統的非正交傳送方法會有一個系統數據速率的臨界轉變值，而這種數值代表，比這個數據速率小的系統，用新的協定會有比較好的效果，反之，還是傳統的非正交傳法會有比較好的效果。而另外一個討論的議題就是功率分配的問題。我們利用中斷概率的數學式算出最佳的功率分配係數來最佳化我們的系統效能。

In this thesis, we consider a cooperative communication system in a wireless network with three nodes and limited by the half-duplex and total power constrained. We discuss two cooperative strategies which mean the Amplify-and-Forward (AF) relaying and Decode-and-forward (DF) relaying in slot-based block-fading environments. We focus on the non-orthogonal transmission which is defined that the source terminal keeps transmission during the whole cooperative time slots. We assume a classical quasi-static slot-based block-fading channel where the channel keeps constant for one time slot and changes the statement during the second time slot. Under this assumption, we proposed a new protocol that the source terminal retransmits the same data during the second time slot. This proposed protocol based on the selective DF and the AF cooperative modes is superior to the previous non-orthogonal scheme for the low spectral efficiency. By the simulation result, there is a boundary system data rate between the proposed protocol and the classical non-orthogonal protocol. Therefore, we may select a suitable mode between the two protocols based on the boundary rate to improve the system performance. Another issue is the optimal power allocation problem. The power allocation strategy uses the expression of the outage probability to optimize the criterion of the power allocation parameters.