近年來，在無線網路中合作式通訊引起了廣泛的討論和研究的興趣，它更被視為一種可增加通訊品質與可靠性的傳輸技術，合作式通訊藉由節點之間的合作來有效建立空間分集。然而考量到實際的通訊系統協定之運作，我們必須要謹慎的在其實體層(PHY)上層作整體化的協定設計(尤其是在媒體存取控制(MAC)層和網路層最為重要)，使此技術的優點得以充分發揮與實現。
在參考文獻中，有作者提出了一個針對合作式無線網路系統的跨層設計架構，此協定命名為CoopGeo，它由兩部分所組成，一個是結合媒體存取控制層及網路層的設計下選出最佳的轉遞點(forwarder)，另一則是結合媒體存取控制層及實體層的設計下選出最合適的中繼點(relay)。而其中繼點選取範圍由於要避免掉盲點暗藏(hidden node)的問題,所以採取了雷諾三角形(Reuleaux triangle)的方法來縮小範圍,但也因此將遺漏掉許多可選取的中繼點。
在此篇論文中，我們延續CoopGeo的架構，針對MAC-PHY跨層做設計，提出一個新的中繼點選取範圍，用於選擇最佳的中繼點。我們利用錯誤率的觀點分析可將此選取範圍用橢圓來表示，並保證所有在橢圓內的候選中繼點皆可提供比直接傳輸(direct transmission)更好的合作式通訊，之後再由這些候選中繼點中選出最佳的中繼點。透過新的中繼點選取範圍，將增加了合作式通訊的機會，然而在完成中繼點選取範圍後，隨之帶來了一個盲點暗藏(hidden node)的問題，我們在此利用媒體存取控制層的封包交換控制來解決。透過電腦模擬分析結果可看出，我們所提出自新中繼點選取範圍中來選取中繼點的傳輸錯誤率表現優於直接傳輸和先前的CoopGeo 協定，而隨後也比較了不同調變方式針對所提出的方法的錯誤率來作比較。

Cooperative communication for wireless networks has gained much attention because the spatial diversity can be achieved by nodes collaboration. However, to take full benefits of cooperative communications in practical networks, higher layer protocols, especially the medium access control (MAC) and network (NWK) layers should be designed carefully.
A framework of cross-layer design for cooperative wireless networks, named CoopGeo, has been proposed in the literature. It is mainly composed of the forwarder and relay selections; the former is a joint MAC-NWK layer design and the latter is a joint MAC-PHY layer design. Nevertheless, to avoid the hidden node problem during the relay selection process, the choice of the relaying area in CoopGeo is based on the Reuleaux triangle graph, naturally leading to a loss of potential relays that are within the source’s transmission range. In this thesis, following the framework of CoopGeo, we propose a new MAC-PHY cross-layer design for relay selection, where the relaying area is modeled as an ellipse graph through a QoS-guaranteed coverage analysis. Specifically, every relay within the ellipse-shaped relaying area can provide a better cooperative link than the direct transmission. The use of the new relaying area, yet, leads to a hidden node problem and hence an increase of the collision probability during the relay selection contention process. We also propose a handshaking mechanism to solve this problem. Simulation results show that, in comparison with CoopGeo, the proposed relay selection scheme significantly improves the symbol error rate (SER) performance over fading channels. Moreover, our scheme also provides better performance in terms of the transmission error probability that is defined to assess the joint error behavior due to collision and channel fading.

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