| Along with the development of white LED technology and its popularity in the lighting field, there has been an emerging wireless optical communication --Visible light communication (VLC). Through driving the white LED modulated by data signal, VLC can provide up to Gigabit rate communications to the indoors equipment. Currently, however, VLC is still in experimental research stage, mainly because of the complex and changing indoor lighting environment, with the constrained LED power and the multipath effects arising from the reflected light path, the channels have emergence of great background noises and inter-symbol interference (ISI), so that the signal-to-noise ratio (SNR) and bit-error rate (BER) of the system can not meet the high-speed, stable and reliable communication requirements really. Based on the concept of multi-input and multi-output (MIMO) VLC system, this paper aimed at reducing noises and crosstalk through the adaptive technology to improve the system performances and to reduce the differences among the multi-user services.Building a practical simulation environment, based on the MIMO-VLC system model and channel analysis, the article shows the LED illumination distribution, the received optical power distribution, and the multipath delay spread distribution, targeted to explain the cause and solutions that the optical power distributed different between positions, the ISI caused by multipath delay, etc.First, the paper presents a novel LED light arrangement, which can smooth the distribution of SNR without hidden corners, so that the system is supplied to users in different locations the equal value communications, the SNR difference jitter as low as 0.8dB obtained by simulation in a reasonable configuration of layout positions and the output power.Secondly, because of the new pattern has more extreme multipath effects, this paper proposed to use time-domain equalization techniques that can reduce ISI. With comparison of zero forcing linear equalizer (ZF) and the adaptively minimum mean square equalizer (LMS) effectiveness, this paper drawn a conclusion that the system can be obtained superior BER performance under ideal equalizer.Furthermore, the article put forward an adaptive equalization technology and a diversity reception technology all based on artificial neural network (ANN), using the multilayer neural networks to solve the binary classification problem, and combining with the multi-input diversity characteristic in MIMO-VLC to achieve channel estimation and adaptive optimization. Research shows that the ANN equalizer in a diversity receiver which with just a few training sequences, then can reach the effect of traditional LMS equalizer, the the higher rate, the more fully utilize the limited difference information to estimate the channel, adaptively enhance the noise resistance and the ability to equalize the crosstalk. It shown that the equalization receiver exhibited excellent performance of maintaining a high speed transmission by a low BER under the harsh SNR, so as to enhance the overall performance of a system with complex channels.Finally, the article proposed the idea of a two-way full-duplex MIMO-VLC system. By modulating individually with the three emitting chip in a white LED, and using a diversity receiver in optical filters receiving three-way channels, the new VLC system can achieve synergy and duplex. With the adaptive Equalization technology, it can make visible light communication has broad application prospects. |
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