隨著急遽增加的網路容量需求，建置一個符合成本效益且能支援高密度用戶區域的網路架構將會是一大挑戰。因此，如何在不改變現有接收端硬體架構的條件下於行動去程網路中增加系統整體傳輸量以及覆蓋範圍是一個主要的研究課題，同時對於未來5G通訊來說也將是一個關鍵的技術。
本論文中我們利用偏振多工技術提升一倍的系統容量，並提出自極化分集之PDM DDO-OFDM系統達到解偏振多工，此架構由被動元件所組成且不需要偏振追蹤機制即，因此有低成本、低複雜度的好處。系統最大的優勢在於可以從ONU端獨立出來，所以能維持現有的硬體架構。我們透過模擬及實作證明系統架構的可行性，此外也針對系統做詳細分析，包括最佳CSPR及launched power的討論。在偏振多工系統中，訊號偏振態會隨著傳輸光纖而隨機變化，因此本論文也探討系統遇到的偏振相關的損害進行討論。

As the soaring demand in channel capacity, establishing a network architecture which meets cost-effectiveness and supports population dense area becomes a big challenge. Therefore, increasing the channel capacity and network convergence for the next generation mobile fronthaul without changing the existing receivers’ design is a hot research topic. These also are key techniques to support the next 5G communications.
In this thesis, we double the system capacity by applying the polarization division multiplexing (PDM) technique with the proposed self-polarization diversity scheme for PDM direct-detection optical orthogonal frequency division multiplexing (DDO-OFDM) system. The proposed polarization de-multiplexing scheme composing of passive components without any polarization tracking mechanism is low-cost and low-complex. Moreover, it can be implemented in the power remote node and thus the existing hardware design at receivers can be retained. We demonstrate the proposed self-polarization diversity PDM DDO-OFDM in both simulation and experience to prove the feasibility of this scheme. Furthermore, we investigate some of important parameters, including the optimization of carrier to signal power ratio (CSPR) and launched power. On the other hand, the polarization state is randomly change during fiber transmission in the polarization multiplexing system. We also discuss the polarization impairments in this scheme.

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