| Summary: | 碩士 === 國立清華大學 === 光電工程研究所 === 105 === 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.
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