全球科技日新月異，行動通訊技術也快速的發展，時至今日，在2020年的此時此刻，第五代行動通訊也正式上線，承襲第四代行動通訊的正交分頻多工(Orthogonal Frequency-Division Multiplexing, OFDM)調變技術，並且著重於三大基礎概念，其中，就大規模機器型通訊(Massive Machine Type Communications, mMTC)的情況而言，其特徵在於連接大量元件設備，約每平方公里內有100萬個裝置的機械間通訊需求，屆時，就前傳分波多工(Ultra Dense Wavelength Division Multiplexing, UDWDM)的系統而言，每個裝置都必須分配到一個特定的波長當作光載波，各自成為一個通道，由於頻譜資源有限，每個波長間距將會變得相當密集，所以在實際情況下，在中央單元(Central Unit, CU)光載波漂移的現象以及在分布式單元(Distributed Unit, DU)濾波器無法乾淨濾出指定通道資訊是容易發生的，此會造成通道響應有不穩定的情形，影響訊號品質。本論文提出利用位元功率分配演算法來動態適應通道響應的改變，在實際的通道響應和有限的接收功率之下，將位元和功率做有效的分配，並且在一定的位元錯誤率門檻之下，盡量達到最高的吞吐量，在通道響應條件改變時，呈現出優化通道能力及舒緩通道變化對訊號破壞的作用。
在實驗架構一中，將呈現前傳之超密集分波多工的架構，利用強度調變與直接接收(intensity modulation/direct detection, IMDD)的方式進行調變與接收正交分頻多工正交振幅調變(Orthogonal Frequency-Division Multiplexing-Quadrature Amplitude Modulation, OFDM-QAM)的訊號，解分波多工是利用光學濾波器進行濾波來達成，藉由改變接收功率、移動濾波器通道位置，來模仿通道響應變動的情況，最後再離線進行數位訊號處理，計算經過位元功率分配演算法之後可以乘載之資料量。在實驗架構二裡，再加入偏振態多工(Polarization-division multiplexing, PDM)結合UDWDM的技術，讓在有限的頻譜資源中提升可傳輸之資料量，不需要進行偏振態追蹤就可以用光學濾波器進行解多工，再來藉由改變光學濾波器來造成不同載波功率比的情況、改變雷射波長模仿載波偏移，並且在遠端無線電站(Remote Radio Head, RRH)端將訊號升頻至28GHz，進行毫米波無線傳輸。最後證實，位元功率分配演算法在UDWDM的系統當中，有機會成為將來動態適應通道的一種方式。

With the rapid growth of technology nowadays, mobile communication technology is popular topic these days, specially in 2020. 5th Generation Mobile Networks is going wild. When it comes to massive Machine Type Communications (mMTC) scenario, large quantity of devices should be connected. 100 million connections of devices per square kilometer is required. In mobile fronthaul Ultra Dense Wavelength Division Multiplexing (UDWDM) system, every device needs specific wavelength as an optical carrier to become an individual channel. Due to limited spectrum resource, the channel spacing of optical carriers will narrow down when the number of device increases. Thus, in real situation, the deviation of laser wavelength at central unit (CU) and imperfection of optical filter at Distributed Unit (DU) are two major reasons to have impacts on channel response, which cause unstable data performance.
In this work, bit and power loading algorithm is used to adapt channel response dynamically in mobile fronthaul UDWDM system. Under the circumstance of real channel response and limited received optical power, bit and power loading algorithm redistributes bits and power effectively so that higher capacity can be achieved under the assigned FEC threshold. When channel response changes, bit and power loading algorithm can have the ability to optimize the data performance and alleviate the signal damage.
In setup one, the experiment of UDWDM is demonstrated. Intensity modulation and direct detection (IM/DD) is used to modulate and receive Orthogonal Frequency-Division Multiplexing-Quadrature Amplitude Modulation (OFDM-QAM) signal. Tunable optical filter is adopted to serve as de-multiplexer to select different channels. In order to mimic the varying channel response, different received optical power and different position of the filter are considered. After that, digital signal processing is carried out to calculate the maximum possible capacity by bit and power loading algorithm.
In setup two, Polarization-division multiplexing (PDM) is introduced to combine with UDWDM system so that more data can be transmitted in limited spectrum resource. In this way, Polarization-tracking is not needed and tunable optical filter is adopted to serve as de-multiplexer as well. Different carrier power ratio and deviation of laser wavelength are considered. At last, signal is up-converted to 28 GHz at Remote Radio Head (RRH) and demonstrate the wireless transmission.

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