現今手機及多媒體服務使用者數量的快速成長已導致手機網路的使用流量過度負
荷，而3GPP制定了資料減量的技術去解決此問題。除此之外，設備對設備通訊也
被視為是解決流量過載的一個新方法，在手機網路架構下的設備對設備通訊可以有
效減少無線存取網路及核心網路的負荷。設備對設備通訊通常是指設備間可以不靠
存取點、基地台及服務提供者就可以自行相互通訊的一種技術。在應用一些特定的
規則及方法之後，設備對設備通訊可以有效的減少手機網路的負荷及增加頻譜使用
率。另外，此篇論文亦採用了中繼傳輸的方式去改善設備對設備通訊網路的效能當
使用者設備之間相距太遠或頻道品質不佳的時候。接著，此篇論文探討了在設備對
設備通訊網路中的中繼站選擇的議題。最後，此篇論文提出了一個在設備對設備通
訊網路中的集中式中繼站選擇演算法。

Nowadays, the explosive development on the number of mobile user and multimedia services
cause a severe traffic overload problem in the cellular network. Data offloading in
the Third-Generation Partnership Project (3GPP) is defined as critical scheme to cope with
this issue. Furthermore, device-to-device (D2D) communications have been considered as a
new data-offloading solution. The D2D communications underlay cellular networks infrastructure
reduces the radio access network load and the core network load. Device-to-device
(D2D) communication commonly refers to a technology that enables devices to communicate
directly without access points, base stations, and wireless operators. With the application of
specific rules and strategies, D2D communications decrease the mobile network load and
increase the spectral efficiency. Moreover, relay assisted transmissions are considered in this
thesis to efficiently improve the performance of relay assisted D2D communications when
D2D user equipments (UEs) are too far away from each other or the quality of the D2D channel
is not good enough for direct communications. Thereafter, the relay selection issues on
D2D communication in cellular network is studied in this thesis. Finally, a centralized relay
selection method for relay assisted D2D communication systems is proposed in this thesis.

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