Study of LED layout in indoor visible light communication and performance analysis

Light emitting diodes(LED) could provide both illumination and data communication in indoor visible light communication(VLC) that owns the modulation bandwith from several from several MHz to seneral hundreds of MHz. The layout of LED plays an important role in maintaining a steady optical power distribution over the receiving plane. The existing rectangular LED layout does not provide a full coverage on the receiving plane leaving receiving optical power outage area, which in turn affects the best performance of the VLC system. This paper design a circular layout scheme of LED in 5mX5mX3m room based on the criterion of the illumination minimum mean square deviation. The influence of the distribution of the intensity of illumination with the radius of 1m and 1.5m,for including the wall reflection and not including the wall reflection, and make a comparison with rectangular LED layout of illumination distribution, when the number of LEDs with rectangular layout as same as circular layout. Including the number of LEDs are 4 and 16.For a specific simulation parameters as following:height of receiving plane is 0.85m,a single LEDs is composed of 60X60 LED chips, the parameters of a single chip is that transmitting power is 20mW,center luminous intensity is 0.73cd. semiangle at half power is 70deg.The parameters of concentrator is that photodiode area is 1cm2,photodiode responsivity is 0.4,field of view at the receiver is 85deg.Other parameters are that reflective index of concentrator is 1.5,reflectivity of wall is 0.8. Circular layout and rectangular layout are analyzed through simulation of the received optical power distribution, signal noise ratio distribution in non line of sight(including the wall reflection) and line of sight(not including the wall reflection),when the number of the LED is different. It is clear from the results that the received optical power distribution of non line of sight is better than line of sight, when the number of the LED are same, but the signal noise ratio distribution is decreased result of the reflection of the wall. It is found that the received optical power of circular layout is better than the received optical power distribution of rectangulr layout, and circular layout is a good solution that add the received optical power at the 4 corners of room, improve the system ability of communication, when making a contrast of rectangular lyout with circular layout,at the same time,the fluctuate of circular layout’s signal to noise ratio of is smller than rectangular layuot.The radius of circular layout or the location of rectangular layout is keeping, the received optical power of receiving plane is increased, by adding the number of LED,in the meantime, the interference between LED light source also increase. But the increase of the circular layout radius when the number of LED remain the same is helpful to reduce the inter symbol interference that work out between LED each other, enhance the system signal noise ratio. In this paper, the results of the reaearch provides a new idea for indoor visible light communication with non-standard room (Size of room is not 5mX5mX3m), at the same time, provides guiding significance for future setting up the indoor visible light communication links.