OFDM無線網路之合作通訊---子計畫二：用戶端合作式正交分頻多工系統之協定設計與分析(I)

Abstract

本整合型研究子計畫旨在瞭解合作通訊在蜂巢系統或是無線隨意網路下、快速時變多路徑衰退通道環境中所扮演的角色。主要想探討的課題為在採用正交分頻多工或正交分頻多重接取調變技術的情形下，固定或移動結點之間可能合作模型之建立、合作協定設計以及相關之效能分析。 合作式通訊主要的觀念在於利用無線通訊系統播放傳送的特性與在想辦法增加分集多樣性的概念下，透過其他用戶端亦即轉接節點的天線來轉接訊號的作法，用以增加空間分集。透過轉接節點的合作來重複傳送來源端信號的機制確實可以增加整體網路系統的容量，避免單一天線傳輸系統中可能遭遇之嚴重衰退效應，造成接收端無法可靠地還原有效的資訊。然而由於行動無線傳輸下所不可避免的不確定性，合作式通訊系統在分析、演算法建立與系統實現上仍由許多困難尚待突破，需要更深入的分析與開發更有效率的訊號處理技術。對此我們提出了三年期的整合計畫來解決此問題。 第一年我們想探討固定節點下之合作式分頻多工系統之實體層通訊機制。主要的研究課題為合作式分頻多工系統之協定建立與分析、用戶節點之間分散式調變與檢測技術研發與合作機制下之多用戶偵測演算法。第二年我們將焦點轉至移動節點下的合作式通訊，建立隨機網路模型與其相關之協定建立與分析。我們在第三年想要探討的主題在於整合消息理論和賽局理論的結果，研究不同節點間如何決定合作或是競爭機制，以達到節點壽命和網路容量的最佳平衡結果，並將前兩年的研究成果擺在此一框架下做完整的比較。

We aim to thoroughly understand the role of cooperative communications in celluar systems or wireless ad hoc networks with fast time-varying frequency selective channels in the subproject. In particular, the main focus lies on, when employing orthogonal frequency division multiplexing (OFDM) and/or orthogonal frequency division multiple access (OFDMA), the research of model development and designs of cooperation protocols with fixed and mobile nodes with performance analysis. The key concept of cooperative communications is the relay of messages by intermediate nodes between source and destination, which exactly exploits the broadcast nature of wireless medium and comes from the idea of increasing diversity sources as possible as one can. This constitutes a virtual multiple antennas transmission network by the use of relay nodes』 antennas and increases the network capacity with appropriate transmission protocols and/or coding schemes such as space-time codes. Although cooperative communications provide a promising means to enhance performance of the system without needing to expand the size of any particular mobile terminal by implementing multiple antennas, there remain challenges to be solved due to the randomness introduced by the wireless mobile network. We propose a three year』s subproject to perform further analyses and develop more efficient signal processing techniques with the emphasis on designs and analyses of cooperative OFDM system physical layer protocols under frequency selective fading. The subproject is outlined in the following. In the first year, we will study physical layer cooperative schemes with OFDM interface with fixed (not moving) nodes. Specifically, designs of PHY protocols with analyses, distributed modulation and detection techniques, and development of multiuser detection algorithms are of our primary interests. In the 2nd year, we will study cooperative schemes with mobile nodes, establish a random network model, and design corresponding cooperative protocols. Finally, we will study the possibility of integrating results from information theory with those from game theory, leveraging the lifetime of a relay node with the network capacity and aiming to decide whether to cooperate or to compete in the relay node. Also, we will conduct thorough comparisons among the research results from all three years under the same framework.