Research On High-speed Visible Light Communication Method And System Based On Milti-color Transmission

Visible light communication(VLC) has been considered as an important supplementary technology of broadband access and short-distance communication in the future, which can provide lots of potential bandwidth, free-license and has no electromagnetic interference. In the field of high-speed visible light communication, the application of equalization and multi-carrier modulation have increased the data rate from single-channel system to Gbit level, and multi-channel multiplexing can further improve the performance of VLC system.Wavelength division multiplexing(WDM) technology is the most practical technology and easy to implement. In the early stage, WDM-VLC system has red, green and blue three channels. In the recent two years, four-channel WDM-VLC system used red, green, blue and yellow LEDs has been reported. However, in terms of visible light band, there is still a lot of room to add channels. WDM-VLC system still has a huge potential.Multi-color transmission is a method that can fully exploit the potential of visible light. It can realize mulit-channel communication by applying WDM technology and single color light. However, because the radiation spectrum of LED has a certain width, a phenomenon of spectral overlapping will occur when the number of channels increasing and channel-spacing decreasing, which result channel crosstalk although optical filters are applied. It will limit the number of available channels in visible band. In addition, the indoor lighting often uses white light. Hence the multi-color communication system should consider the color control of mixed light.To solve these problems, we analyze the capacity of multi-color communication system and proposed two methods of color control on the base of introducing basic theory of indoor VLC and colorimetry. The two methods are tune DC bias + OOK modulation and dimming modulation.Through the analysis of multi-color VLC system, the results show that, with on-off keying(OOK) modulation at a BER of 10-6, the multi-color VLC system could most have 12 channels with the channel spacing of 33 nm. The data rate can be increase by decrease channels, because the channel crosstalk is decrease. Considering the data rate limitation caused by LED modulation bandwidth the optimal number of channels is 10 and the data rate is about 9.3 times compared with single channel system. A four-color transmission, white light output VLC system is implemented by using tune DC bias + OOK modulation. The distance of transmission is 1m and data rate achieve 1Gbps+ with BER=10-6. The CIE1931 xy color coordinates of output light is(0.3330, 0.3331). Another four-color transmission, white light output verification system is set up by using dimming modulation. A MPPM dimming modulation scheme is designed by research LEDs’ color characteristic. The experiment results show that the CIE1931 xy color coordinates of output light is(0.3319, 0.3353) when data rate is 7Mbps+, and the chromatic aberration indecipherable for human eyes. It proves the feasible of dimming modulation method.