多載波分碼多址於可見光通訊系統之應用

Application of Visible Light Communication System for Multicarrier Code Division Multiple Access

陳德樺(De-Hua Chen)

指導教授 ： 馮開明

國立清華大學/電機資訊學院/光電工程研究所/碩士(2017年)

摘要

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。

關鍵字

可見光通訊 ； 多載波分碼多址 ； 發光二極體 ； 等化器

並列摘要

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.

並列關鍵字

visible light communication ； MC-CDMA ； LED ； equalizer

參考文獻

[1] Tsonev, D., et al., A 3-Gb/s Single-LED OFDM-Based Wireless VLC Link Using a Gallium Nitride uLED. IEEE Photonics Technology Letters, 2014. 26(7): p. 637-640.

[2] Vučić, J., et al. 230 Mbit/s via a wireless visible-light link based on OOK modulation of phosphorescent white LEDs. in 2010 Conference on Optical Fiber Communication (OFC/NFOEC), collocated National Fiber Optic Engineers Conference. 2010.

[5] Wu, L., et al., Adaptive Modulation Schemes for Visible Light Communications. Journal of Lightwave Technology, 2015. 33(1): p. 117-125.

[6] Huang, X., et al., A Gb/s VLC Transmission Using Hardware Preequalization Circuit. IEEE Photonics Technology Letters, 2015. 27(18): p. 1915-1918.

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