在裝置對裝置通訊(Device-to-Device communications)的系統中，D2D pairs能夠與CUE(cellular user equipment)同時共用一段頻譜資源，並且D2D pair的傳輸不須透過基地台(Base Station, BS)即可直接通訊，如此一來能提高通訊系統的頻譜使用效率、服務裝置數量，然而共用頻譜資源的裝置會彼此干擾，因此在頻譜資源與傳輸功率的分配上必須加以監控，才能建立穩定良好的通訊。DD2D的裝置通常是無線且具移動性，因此D2D的傳送端與接收端的距離也會隨之改變，而距離的遠近也時常會對通道增益的強弱造成影響。本篇論文將探討在滿足CUE的最小速率要求之下，針對不同距離的D2D提出的功率分配的方法，讓所有裝置可以達成穩定的傳輸。針對距離較短的D2D們，我們讓他們已全雙工的方式傳送，並設法讓達成最大的能源效率，本問題是一個分式非線性問題，現有方法難以直接算出最佳解，所以我們利用Dinkelbach’s method搭配迭代法，並且在每一次迭代中把問題連續近似成凹函數優化(Convex Optimization)問題。而對於距離較長的D2D們，我們則讓他們尋找一個相鄰的CUE當作中繼點，讓此CUE幫忙轉送資料，使得連線可以順利建立，同時最大化D2D的傳送速率。根據實驗的結果，我們的方法能夠使短距離的D2D在能源效率上表現良好，在長距離的D2D傳輸速率表現上，也優秀於不經CUE轉送的方式。

In future 5G network, the number of devices is expected to get an explosivegrowth. D2D (Device-to-Device) communication is regarded as an important tech-nique to support 5G. It allows D2D pair to reuse cellular user equipment’s (CUE)resource block (RB) and transmit data in the same time, spectral efficiency willget increased. However, the devices reuse same RB will cause interference toeach other. Therefore, the power allocation strategy is very important for D2Dcommunication.In this thesis, we assume that the distance between D2D transmitter and re-ceiver may be different. We divide D2D pairs into two categories: short-distanceand long-distance. For short-distance D2D pairs, we let them communicate di-rectly then try to maximize energy efficiency (EE). For long-distance D2D pairs,they may not be able to build a stable connection due to bad channel condition.Therefore we let them find a CUE as a relay to transmit data from D2D pairsand try to maximize the data rate of D2D pairs. Simulation results show that ourmethod can achieve good EE for short-distance D2D pairs. For long-distance D2Dpairs, data rate through CUE assisted performs better than transmit directly.

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