| Visible light communication(VLC)technology combines lighting and communication technologies,satisfies the needs of green energy while transmitting data.Visible light communication technology based on Light-emitting diode(LED)can utilize free spectrum and low-cost emissions to provide a communication system with high signal-to-noise ratio and achieve high modulation power.Higher data transfer rates can be achieved to alleviate the current shortage of radio frequency(RF)spectrum resources.Visible light communication is a broadband wireless access technology,which has the advantages of rich spectrum resources,large potential communication capacity,good confidentiality,green,safe and no need of license.However,in practice,the modulation degree of LED in visible light communication system is narrow,and the modulation bandwidth is limited.Therefore,various methods and techniques for improving the rate and network capacity of the VLC system need to be studied to achieve the goal of high-speed communication.The non-ideal transmission characteristics of visible light communication systems impede the development of visible light communication technology in terms of transmission rate and communication error rate,especially the application of visible light in the field of high-speed wireless optical communication.Channel equalization refers to an anti-fading measure taken to improve the transmission performance of a communication system in a fading channel.It is mainly used to eliminate or reduce inter-symbol interference caused by multipath delay in broadband communication.To this end,three equalization schemes for non-ideal transmission characteristics of visible light are proposed:ˇA visible light communication equalization scheme based on the least mean square algorithm is proposed.In a common VLC communication system,there are generally multiple receivers and multiple transmitters,due to the disadvantage of LED and noises from other light,it generates time-varying characteristics and serious inter-symbol interference.An appropriate equalization technique can effectively reduce the inter-symbol interference,the non-ideal transmission characteristics can be reduced much.The scheme is designed based on the least mean square algorithm equalizer.The structure and coefficient of the filter are optimized by the training sequence.The simulation results show that the ratio of the scheme can achieve 10MHz,and the rate of error is lower than 10-',the convergence performance of the original conventional algorithm is also improved.ˇ A visible light communication equalization scheme based on radial basis function neural network is proposed.The irrational transmission characteristics of visible light communication technology is actually a nonlinear problem,which can be well solved by neural network technology.As a nonlinear dynamic structure,the neural network can process its large-scale data quickly while transmitting data at high speed in the visible light communication system.For data stream in system,the function of equalizer can be regarded as the auxiliary for signal decision.The decision makes use of the classification ability of the neural network to balance the nonlinearity in visible light communication,which can reduce the bit error rate of the signal and effectively reduce its non-ideal transmission characteristics.Experimental results show that the scheme can achieve better effect than the conventional equalizer,and also has a simple network structure and excellent convergence performance.ˇDesigned and implemented a visible light communication system with joint synergy equalizer for LED multi-lamp array.There are two core devices in the visible light communication system.One is the photodetector at the receiving end,which converts the optical signal into an electrical signal,and the other is the LED at the transmitting end,which emits an optical signal.Among them,LEDs are originally designed for lighting.They are normally arrayed for application,which can ensure the illumination demand and transmission stability.However,in actual communication systems,the spatial characteristics of LED cause some trouble.In an indoor visible light communication network,the LEDs in different positions in the array have different channel characteristics.The research designed and implemented a synergy-equalized visible light communication system for the different channel characteristics in LEDs array which reduces the non-ideal transmission characteristics of visible light communication. |
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