The Study Of Antenna Layout In Visible Light Communication

In order to improve system capacity,researchers introduce multiple input multiple output(MIMO)technology in visible light communication(VLC).However,MIMO technology can improve channel capacity,but it also brings inter-channel interference(ICI).Therefore,MIMO VLC system performance deteriorates seriously.ICI is strongly influenced by channel transmission matrix,and the channel transmission matrix is closely related with antenna parameters.So,this article optimizes the MIMO VLC system performance by adjusting the antenna parameters.There are many studies on VLC antenna layout,but merely consider the receiver antennas located at the center of the room.However,in practical scenario,the receiver antennas may be placed at any location in the room.So,we extend the placement range of receiver antennas from center of.the room to the whole indoor plane.Then we introduce several circular layouts and latticed layouts,and analyze the contour distribution characteristics of channel capacity in the whole indoor plane.The simulation results show that,the channel capacity of MIMO VLC system is not only affected by the distance between light emitting diodes(LEDs)and the distance between photo detectors(PDs),but also by the positions of antennas.In addition,in lattice layout,the distribution characteristic of channel capacity is related with antenna layout.But there is no relationship between channel capacity and antenna layout in circular layouts.At the same time,the simulation results also show that,there are high ICI in MIMO channel at the center of the indoor plane.In order to decrease even eliminate ICI,we introduce two power allocation schemes.These two schemes all keep the total power constant but change the proportion among each channel.Then we calculate channel capacity of a 9x9 system and a 10×10 system by using these two power allocation schemes,and analyze the impact of allocation scheme on system performance respectively.The simulation results show that,these two schemes can optimize the system performance in different degrees.The first scheme can decrease the fluctuation degree of capacity curve but cannot eliminate deterioration.Comparing to the first scheme,the second scheme has a higher capacity and a smoother capacity curve.Monte Carlo method is one of the high accuracy numerical computation methods,but it needs numerous samples to estimate the expectation of random variable.So,its calculation amount is inevitably tremendous.Aiming at resolve the contradiction between computational accuracy and calculation amount,we introduce an "analysis method" to calculate channel capacity.This method deduces the asymptotic expression of mutual information at first,and then obtains the maximum of mutual information,which also named channel capacity.In order to validate;"analysis method",we use the"analysis method" to analyze the channel capacity of a 8x8 system and a 10x10 system,and make a comparison with the Monte Carlo method.The simulation results show that when SNR changes,the "analysis method" can describe the variation tendency and calculate the maximum value,as well as significantly reduce the running time.So,this article offers a new way to calculate channel capacity with low computation.