Research On High-speed And Dimming Control Visible Light Communication

VLC is an optical wireless communication system with short distance transmission, by using LED as light source. Compared with traditional light source, such as incandescent lamp and fluorescent lamp, LED has some advantages, for example, long life, low power consumption, less heat. Besides, an important feature of the LED is that it can be modulated, which can combine data transmission and lighting.In the study of information transmission, the lower frequency bandwidth greatly limits the data rate. In order to improve the data rate, single visible light communication and multi-channel visible light communication has been studied. Though the data rate of single channel VLC has been improved much, it is still potential according to the new research. In addition, the data rate of real-time multi-channel VLC relies on modulation methods to expand the channel number, while the research on the one channel of multi-channel is weak. Thus, it is of important significance to apply the data rate improvement method of single channel to multi-channel VLC system. In the study of lighting research, variable on-off keying(VOOK), variable pulse position modulation(VPPM), multi-pulse position modulation(MPPM), overlapping pulse position modulation(OPPM) are used in single channel VLC to dim the light, while the research in multi-channel VLC system is poor.To solve the problem above, some solutions are presented under the premise of full investigation in this paper.. At first, the basic principle of VLC is analyzed. Next, broadband photoelectric conversion circuit is designed to reduce the cost. Then, new design of high-speed equalization circuit is proposed, which achieve a substantial increase of the data rate in the RGB LEDs system. And it also provides reliable technology for CSK system. At last, a novel modulation is presented combined with CSK, which improves the performance.The broadband photoelectric conversion circuit has a gain of 104 and a bandwidth of 123 MHz by designing high-speed current voltage conversion circuit and first-stage differential amplifier circuit. The bandwidths of RGB LEDs are increased to 483 MHz, 331 MHz and 352 MHz by using the designed equalization circuit. At the bit error rate(BER) of 10-4, the data rate of RGB can reach 770 Mbps, 740 Mbps and 770 Mbps. At the BER of 10-6, the data rate of RGB can reach 750 Mbps, 730 Mbps and 750 Mbps. At the BER of 10-9, the data rate of RGB can reach 710 Mbps, 660 Mbps and 700 Mbps, which is superior to the current result of 550 Mbps in the world and provides the foundation for the improvement of data rate in CSK system. What’s more, high-speed variable pulse modulation is proposed. Combined with CSK modulation, it simplifies the strict synchronization problem of CSK and provides the dimming control function. The effect of key parameter on bandwidth utilization ratio and BER is analyzed. The simulation results shows that the HVPM-CSK VLC modulation has a better performance than VOOK, VPPM and MPPM in the limited band and signal noise ratio(SNR).