Optimization Of Light Sources Layout In Visible Light Communication System Of Coal Mine Working Face

The environment of underground coal mines is very complicated and special.Coal mine working face is an important area with a large number of mechanical equipments and staff members.With constant driving of shearers,the space is a variable communication space.In recent years,the rapid development of visible light communication technology belongs to short-range wireless communication technology.The received optical signal decays rapidly with the increase of transmission distance and mainly comes from direct light irradiation.And the visible light communication system can provide communication and underground illumination.In this paper,the major issues of light source layout optimization in visible light communication system of coal mine working face are studied.Considering the special shape of the coal mine working face for communication,a number of light source points for the combined joint effect,the line of sight from light sources and a reflection,secondary reflection or three reflections from coal walls,hydraulic support,coal mining equipment,a model of visible light communication system in coal mine face was established with the use of ray tracing method.Aiming at the problem of inhomogeneous distribution of optical signals in the surface of visible light communication system,the improved method of optimizing the power of the LED light source was proposed,and the signal-to-noise ratio factor was used to measure the signal-to-noise ratio uniformity on reception plane.According to the problem of rectangular space communication space with many equal power light source points,the SNR of optical signal in most of the middle position was uniform and the SNR in edge area was small.The power adjustment method based on edge power optimization was designed.Compared with equal power light sources,SNR factor on the receiver plane was reduced by 52.7%.To further improving receiver plane signal to noise ratio uniformity,swarm optimization algorithm,fireworks algorithm was applied to optimize the power of each LED light source in paper.Compared with the same power light sources,the signal to noise ratio factor on the receiver plane was decreased by 60.4%.Aiming at the sensitivity of light source power attenuation to distance in visible light communication,a method of optimizing height and two-dimensional position distribution of each LED light source was proposed to improve the uniformity of signal-to-noise ratio on receiver plane.When all LED light sources were distributed with uniform array,the spatial height of each light source was optimized with fireworks algorithm to decrease the SNR fluctuation on the receiver plane.The signal to noise ratio factor on the receiver plane reduced by 50.1% after the light source height was optimized with no limit with 80 LEDs in VLC system.When the light source height is limited in the range of 2.6 to 3 meters,the signal to noise ratio factor on the receiver plane reduced by 32.8% after the light source height was optimized compared with uniform array of 80 LEDS.For some certain circumstances,the light sources must be instal LED on the top of communication space and the number of light sources could be set as needed.According to the number of light sources,the fireworks algorithm is used to optimize the two-dimensional position of each light source.The more the number of light sources is,the smaller the value of the received signal SNR is.When the total number of LED was 80,The noise to ratio factor is 32% lower than the array distribution.In the progress of optimization,the initial value of the same height distribution or the uniform array distribution was replaced by the initial value generated randomly to improve the iteration efficiency.According to two conditions of the height limited and unrestricted of LED light sources,the optimization method of three-dimensional space position optimization was designed to improve the uniformity of signal-to-noise ratio.After three-dimensional position optimization,compared with the two-dimensional optimization,the signal to noise ratio factor slightly reduced when the number of LED light sources was 45.The signal to noise ratio factor decreased by 49.5% than the uniform array distribution of light sources.Experiments show that the signal to noise ratio factor could be significantly reduced with the two-dimensional position or three-dimensional position optimization of light sources.