在可見光通訊系統中，由於LED燈具的頻率響應不良，使用OFDM時會使某些頻段無法使用，使得可用頻寬大幅降低，如果使用adaptive OFDM或是pre-equalizer OFDM則會使系統的複雜度上升。而在LED的選擇上可以分為螢光粉LED與RGB-LED，RGB-LED的頻率響應優於螢光粉LED，但是在價格上會高出螢光粉LED許多。由於這兩個原因不符合可見光通訊的初衷，也就是價格便宜且複雜度低這兩大原因，於是在本論文中，提出使用螢光粉LED並且使用MC-CDMA技術，將所有子載波進行正交編碼，讓所有的子載波共同承擔頻率響應較差的頻段，使以螢光粉LED為光源的可見光通訊系統可以達到更好的表現。
在本論文中，我們使用螢光粉LED來傳輸MC-CDMA訊號，經過兩公尺的可見光無線傳輸後，在接收後使用MMSE等化器並且結合多碼干擾消除演算法，使接收表現能夠有進一步的提升。在實驗中，使用MC-CDMA訊號可以把原本30MHz頻寬的訊號給拓展到60MHz頻寬，是原本OFDM訊號的兩倍。

The bandwidth of LED is commonly ranged from several MHz to 20 MHz. When we use orthogonal frequency division multiplexing (OFDM), because the LED frequency response is very poor, there will be some frequency band unusable at visible light communication (VLC) System. If we use adaptive OFDM or pre-equalizer that will increase the complexity of the system. LED can be mainly categorized as phosphor-based LED and red-green-blue (RGB) LED. RGB LED has a wider modulation bandwidth, but it costs much more than a phosphor-based LED. Based on these two points, we proposed a multicarrier code division multiple access (MC-CDMA) signal to equalize subcarrier performance via encrypting all subcarriers with various orthogonal codes of the phosphor-based LED VLC system. In this way, all subcarriers share the effects from poor frequency bands and thus the phosphor-based LED VLC system can achieve better performance.
In this thesis, we use the phosphor-based LED to transmit the MC-CDMA signal. After two-meter VLC transmission. We apply minimum mean square error (MMSE) equalizer and multi-code interference (MCI) cancellation algorithm to enhanced system performance. In our experiment results, we largely enhance the communication bandwidth form 30MHz to 60MHz, which improvement of the modulation bandwidth is up to 2 times in VLC system using a phosphor-based LED.

中文摘要 i
ABSTRACT ii
致謝 iii
目錄 iv
圖目錄 vi
表目錄 viii
第一章 緒論 1
1.1 前言 1
1.2 研究目的與動機 2
1.3 論文架構 3
第二章 可見光通訊系統 4
2.1 LED基本介紹 4
2.1.1 LED發光原理 4
2.1.2 白光LED 5
2.1.3 LED調變方式 7
2.2 光偵測器介紹 9
第三章 多載波多碼分址系統 10
3.1正交分頻多工(OFDM)系統 10
3.2分碼多址(CDMA)系統 12
3.2-1多址傳輸系統 12
3.2-2 CDMA加碼與解碼 15
3.3多載波分碼多址(MC-CDMA)系統 17
3.4 OFDM與MC-CDMA之頻寬容量 19
第四章 接收端之設計 21
4.1接收端等化器 21
4.1.1強制歸零等化器(Zero Force, ZF) 22
4.1.2最小均方誤差等化器(MMSE) 23
4.2多碼干擾消去(MCI cancellation) 24
第五章 可見光通訊實驗 26
5.1可見光通訊實驗架構 26
5.2 LED燈具電壓之最佳化 27
5.3使用DSP前之實驗結果 29
5.3.1 各頻寬之subcarrier vs. BER圖 29
5.3.2整體系統表現 32
5.4使用DSP後之實驗結果 41
5.4.1 各頻寬之subcarrier vs. BER圖 41
5.4.2整體系統表現 43
5.5整體實驗結果 47
第六章 結論 53
參考文獻 54

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