Design of Device-to-Device Communications for Intra-eNB Traffic in LTE-A Networks

[[abstract]]LTE (Long Term Evolution)，是由3GPP所制定的的第四代無線行動通訊，為了解決LTE基地台 (Evolved NodeB, eNB)在無線訊號覆蓋範圍邊緣訊號強度不足，基於佈建成本考量等問題，3GPP提出LTE-Advanced架構，制定了低耗電、低成本的中繼節點 (Relay Node, RN)，來增強使用者設備 (User Equipment, UE)在無線訊號覆蓋範圍邊緣的連線品質。 以現在智慧型行動裝置普及率高的情形下，人們可以在任何時間，任何地點進行資料傳輸，使得資料的傳輸量也相當龐大，因此會造成核心網路的負擔。在LTE/LTE-A網路環境下，既使距離相近的兩個UE之間要進行資料傳輸，必須繞經核心網路才能夠運行，若使用Device-to-Device (D2D)通訊，位置相近的兩個UE能夠直接性的傳輸資料，而非繞經核心網路進行傳輸，以減少資料進入核心網路的負載問題。由於D2D通訊的使用前提是兩個UE之間的距離相近，才有機會使用D2D，本文提出了兩種機制去判斷在LTE-A環境下，D2D適合的切換時機點，第一種是以Capacity的角度，根據Cellular和D2D兩種通訊方式的Capacity進行比較，稱為Capacity-based D2D。第二種為進一步將Load加入判斷基準，衍生出Delay-based D2D。模擬結果呈現了基於Intra-eNB做出的效能結果，顯示出使用D2D通訊相對於傳統傳輸型態可以減少傳輸delay，並且有更好的throughput，也節省了資源上的使用量。[[abstract]]Long Term Evolution is one of 3rd Generation Partnership Project (3GPP) standards developed as a fourth-generation mobile communications standard. In order to solve signal strength problem when the user equipment (UE) located at the edge of the signal coverage of LTE base station (Evolved NodeB, eNB), a new entity called relay node (RN) was introduced in LTE-Advanced by 3GPP. RN has low-power, low-cost features that can be used to enlarge the eNB radio signal coverage. Nowadays, smart mobile device becomes more popular, people can transmit information at any time and any place, so that the amount of data transmission is quite large. Therefore, it may cause the overload of core network. In LTE/LTE-A networks, even if two UEs are closed enough and have data to be exchanged, it must go around core network when transmiting data. If Device-to-Device (D2D) communications used, two nearby UEs can directly exchange data, rather than passing core network to reduce loading of core network. This thesis proposes two mechanisms, Capacity-based and Load-based, to assist the decision about D2D or Cellular transmission. Simulation results show that the proposed D2D mechanism not only reduces the transmission delay but also improves the throughput compared to Cellular mechanism.[[note]]碩