Capacity Analysis And Power Distribution Of Visible Light Communication Systems

VLC(visible light communication),as an effective supplement to traditional wireless communication,has become one of the hot spots in the field of wireless communication in recent years.Due to the non-negativity of visible light communication system signals,capacity analysis is no longer as simple as a conventional wireless communication system.In this paper,the issue of capacity and power distribution of visible light communication system is studied.The main work is composed of the following four parts:First,the expression of channel capacity of SISO 2-PAM VLC is deduced.Under the two limitations of limited peak optical signal intensity and constant optical power,and When the transmitted signal is second-order modulated,the system channel capacity expression is deduced by proving the two properties of the entropy function.The probability distribution is given when the channel capacity is maximized,and the correlation is analyzed when the maximum optical power is limited.The result shows the channel capacity of the VLC system can be achieved in the second-order modulation when the probability of two points is 0.5 and the two points are the maximum value and the minimum value,respectively.Secondly,the capacity of SISO 3-PAM VLC channel is analyzed.Under the condition of the peak of optical signal intensity is limited,the channel capacity expression of the system is derived when there is no maximum optical power constraint and maximum optical power constraint,respectively.The probability distribution is given when the channel capacity is maximized.In the third-order modulation,the result shows the channel capacity of the VLC system can be achieved when the three-point probabilities are both 1/3 and the three-point distribution is reachable maxima,median and minimum,respectively.Thirdly,the transmission power allocation problem of parallel MIMO 2-PAM VLC channel is solved.Under the two conditions of satisfying the limited peak value of optical signal intensity and the constant optical power,this paper gets the representation of mathematical expressions through mathematical analysis,and then solves the problem by genetic algorithm.For second-order modulated MIMO VLC channels,the result shows the power allocation is related to the channel gain coefficient for common channels with different channel gain coefficients.For channels with too small a gain coefficient,the channel will not be used to deliver Information,and if the channel gain coefficient difference is not too large,then small gain coefficient should allocate more power,large gain coefficient should allocate less power,resulting in each channel's channel capacity equal to make the entire system channel capacity to reach the maximum.Fourth,the capacity of MIMO 2-PAM VLC system is deduced.Under the two limitations of limited peak optical signal intensity and constant optical power,the expression of channel capacity of optical communication system is deduced by based on the "parallel decomposition of MIMO channel" and the properties of the entropy function.