在第四代行動通訊中使用投機分散式空時編碼暨合作式自動重傳機制之跨層吞吐率分析

Abstract

在此篇論文中，主要是從跨層設計－實體層(PHY)和媒介擷取控制層 (MAC)的角度去分析使用投機分散式空時編碼暨合作式自動重傳機制時的 系統效能。為了能夠確實模擬分析媒介擷取控制層上的封包傳遞行為，針 對投機分散式空時編碼暨合作式自動重傳機制，本篇論文在媒介擷取控制 層提出了相容於4G網路(WiMAX)的通訊協定。此外，當使用投機分散式空 時編碼(ODSTC; opportunistic distributed space-time code)技術進行傳輸時， 時變衰退通道(time-varying fading channel)對於系統效能的影響在本篇論文 中也會納入考慮，因此，若傳輸時節點間的交涉協商延遲(negotiating delay) 大於通道的同調時間(coherence time)時，投機多樣性 (opportunistic diversity) 的好處便無法完全地得到。從模擬結果可以發現，投機增益(opportunistic gain)只有當資料傳輸是在緩慢衰減通道中進行時才會存在。此外，從模擬 結果也可以發現，當資料是在緩慢衰減通道中傳輸時，使用投機式阿拉蒙 特時空編碼 (opportunistic Alamouti's Space-Time Code)來傳輸就能達到不 錯的傳輸效能。相對於緩慢衰減通道，當資料是在快速衰減通道中傳輸時， 使用投機中繼傳輸(opportunistic relaying)並不是一個有效率的方法，因此， 在此情況下，隨機選擇(random selection)中繼站(RS; relay station)來進行傳輸 是較為建議的方法。

The thesis investigates the performance of cooperative Automatic-Repeat-reQuest protocol (ARQ) with the opportunistic distributed space-time coding scheme from the perspective of the cross-layer (Media Access Control, MAC, layer and Physical, PHY, layer) design. Based on the concept of opportunistic relaying for ARQ, the corresponding MAC protocols which are compatible to the WiMAX relay-assisted network are proposed in this work. In addition, the time-varying fading channel is considered when using the ODSTC scheme. Thus, the full opportunistic diversity possibly is not available when the negotiating delay is greater than the channel coherence interval. The simulation results show that the opportunistic gain only exists in slow fading channel, and using distributed Alamouti code is good enough through exploiting the opportunistic gain. On the other hand, the opportunistic relaying is not an efficiency scheme in fast fading channel. Therefore, random selection for choosing RS is recommended when the fading effect is serious.