多中繼點協作式時空編碼傳輸架構的功率配置最佳化

Abstract

協作通信(Cooperative Communications)提供了一種能在多用戶環境下對抗衰減的有效方法。藉由協調數個單天線行動通訊系統(Mobile)使得他們的天線可以被有效率的共同使用及建立一個虛擬的多輸入多輸出陣列，這種新的技術不但可以萃取傳送差異，而且還可以提高無線傳輸的品質。然而，在ㄧ個資源受限的無線網路，此技術的效能取決於系統採用的功率配置方法。 在本篇論文中，我們首先討論協作通信的基本原理。接下來，我們探討將一種名為時空編碼(Space-Time Block Codes)的多輸入多輸出通道容量提升技術(MIMO capacity enhancement technique)併入協作式中繼系統(Cooperative Relaying System)的可能性。然後，在兩種不同的情況下：一種事發送端有通道知識，一種則是發送端沒有通道知識，我們分析放大前向(amplify-and-forward)中繼協定和解碼前向(decode-and-forward)中繼協定的功率配置最佳化。接著，我們介紹一種受到功率限制下，採用時空編碼且擁有雙中繼點的非再生中繼系統(non-regenerative relaying system)的功率配置方法[10]。雖然模擬結果顯示在有或沒有直接訊號的協助下，此功率配置方法優於均分功率配置方法，它依然有諸多限制。最後，我們提出可以使中繼點互相傳送訊息的一個新的功率配置方法。也因此藉由這個方法，我們可以利用使用者協作傳輸(user cooperative transmission)去萃取使用者協作差異(user cooperative diversity)。模擬結果顯示了我們的功率配置方法有若干的優勢。

Cooperative communications offer an effective way to mitigate fading under multi-user environment. By coordinating numerous single-antenna mobiles to share their antennas efficiently and establish a virtual Multiple-Input-Multiple-Output (MIMO) array, not only can this new class of techniques extract transmit diversity, it can also enhance the transmission quality. However, in a resource-constrained wireless network, the performance varies greatly depending on the effectiveness of power allocation strategy. Meanwhile, it has been proven that MIMO capacity enhancement techniques such as Space-Time Block Codes (STBC) can be incorporated into cooperative relaying system to achieve full-rate and full-diversity data transmission. Needless to say, efficient power allocation among mobile users is necessary in order to reap the benefits of cooperative communications. In this thesis, we first discuss the fundamental principles of cooperative communications. Next, we explore the possibilities of incorporating a MIMO capacity enhancement technique known as Space-Time Block Codes (STBC) into cooperative relaying system. Then, the power allocation (PA) strategy for both amplify-and-forward relay protocol and decode-and-forward relay protocol are analyzed under two cases: with and without channel knowledge at the transmitter. After that, we document the power allocation scheme between two relay stations under power constraint for a non-regenerative relaying system based on STBC [10]. Although numerical results demonstrate that this PA scheme outperforms uniform PA scheme with or without diversity path signal, it is subjected to several constraints. Finally, we propose a novel power allocation scheme that enables the two relays to communicate with each other. Thus, user cooperative transmission can be exploited to extract user cooperative diversity. Finally, simulation and analysis results are presented to demonstrate the advantages of our proposed PA scheme.