在本篇論文中，設計並實現了一個水下可見光無線通訊(Underwater
Wireless Optical Communication)收發機。整體系統設計架構基於直流偏置光
正交分頻多工(DCO-OFDM)並搭配紅色發光二極體(LED)與光偵測二極體(PD)，能
夠在一定傳輸距離內，不論傳輸環境為空氣或水中，皆能夠達到最高每秒2 千4
百萬位元的傳輸速率。
水下可見光無線通訊系統與工研院(ITRI)一同合作完成，工研院主要負責前
端模組、乙太網路、數位類比轉換器以及燈具等部分，本篇論文內容則針對基頻
收發機電路的設計以及水下通道模擬這兩部分。收發機的設計採用16 正交振幅
調變技術(16-QAM)，總共使用1024 個子載波以及長度為其1/16 的循環字首
(Cyclic Prefix)。在接收端支援訊號起始點的偵測，並利用數位自動增益控制
(Digital Automatic Gain Control) 技術，降低接收訊號可能因為傳輸距離改
變而大幅影響傳輸品質的問題，增加系統設置的彈性。除此之外，接收端也針對
收發兩端取樣時脈差異(Sampling Clock Offset)造成的訊號相位偏轉進行補償，並根據估測之通道響應結果使用與一階等化器相比，效能更加優化的適應性最小均方等化器(Least Mean Square Equalizer)補償通道影響。通道模擬部分的分析採用蒙地卡羅方法(Monte Carlo Method)，根據給定的參數數值，模擬光粒子在水下通道的傳輸情況以求得訊號強度在不同水質下的訊號衰減幅度，及其對應
的通道脈衝響應(Impulse Response)，得到了水下通到在濁度不高的情況下受符
號間干擾程度較小(Inter-symbol Interference)，並將模擬結果做為接收端演
算法改良的依據。
經實驗結果證實，設計與實現的收發機不論在通道是由空氣或水組成的情況
下都能夠透過紅色發光二極體順利傳輸有效訊號，最高傳輸速率可達每秒2 千4
百萬位元，在傳輸影片的測試中能夠正確無誤的支援720p 高解析度影片傳輸，
並且在一定的範圍內隨意變更傳輸距離都不會影響影片播放的順暢度。

In this thesis, an underwater wireless optical communication (UWOC) transceiver is designed and implemented. The proposed system is based on the DC-bias optical orthogonal frequency division multiplexing (DCO-OFDM) using red LED and PD. The highest data rate achievable is 24 Mbps within a short range no matter transmitted signal in the air or underwater.
The proposed UWOC transceiver is in cooperation with Industrial Technology Research Institute (ITRI). ITRI is responsible for front-end modules, Ethernet connection, analog-todigital
converter/digital-to-analog converter (ADC/DAC) and the optoelectronic devices. In this thesis, the design and implementation of the baseband transceiver and the channel modeling for underwater environment are focused. The design of the transceiver applied 16 quadrature amplitude modulation (16-QAM), IFFT/FFT with 1024 sub-carriers and a CP length equals to 1/16 of the FFT size. Furthermore, with the starting point detection at the receiver part, a digital automatic gain control (DAGC) is designed and implemented to alleviate the signal fluctuation caused by the variation of transmission distance. In addition, SCO compensation and channel equalization are employed at the receiver. An adaptive least mean square (LMS) equalizer instead of traditional least square (LS) equalizer is designed and implemented to achieve better performance. For the channel modeling for underwater scenarios, Monte Carlo method is adopted to simulate the propagation of photons underwater based on
the given parameters. Finally, the signal attenuation and the channel impulse response are derived according to the simulation. The result of the simulation exhibits that inter-symbol interference (ISI) is not severe unless in high turbidity condition.
Based on the verification and evaluation on field programmable gate array (FPGA), the proposed transceiver is capable to transmit data using red LED either in the air or underwater. A 720p high definition video can be displayed at data rate 24 Mbps without any error. Furthermore, within certain transmission range, the video display remains steady and stable.

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