Research On Channel Decorrelation Technologies For Visible Light Communications Based On Array

Visible light communication(VLC)system is a natural array transmission system,so using the multi-lights work in parallel to achieve high-speed wireless access is unique advantages of visible light communications.However,due to VLC technology using intensity modulation/direct detection,ignoring the light wave phase and frequency information.So with the increase in the number of elements,VLC system will have a strong channel correlation,and then this becomes a bottleneck in the realization of ultra-high speed technology for visible light communications.In this paper,based on analyzing the influence factors of the array visible light communication channel correlation,it studies the channel decorrelation technology from the optical domain and the signal domain to reduce the correlation of the channel and improve the reuse gain.The main work of this paper is as follows:1.This paper considers the response characteristics of the array VLC electrical-optical-electrical channel and the equivalent channel model,analyzes the influence factors of the visible channel correlation,and establishes the performance criteria of channel correlation.According to the typical application scenario of visible light communication,the line-of-sight(LOS)link channel model of array visible light communication is established.On this basis,this paper presents some criteria of the correlation performance,such as the channel matrix rank,matrix condition,channel capacity,maximum interference signal ratio and so on.The simulation results show that the channel correlation can be effectively reduced by adjusting the pitch of transmit-receive element and the vector direction of the array element.2.Aiming at the problem that the array VLC channels is highly correlated,this paper proposes an optimization method about channel matrix rank based on the spatial structure of transceiver array,which effectively improves the reuse gain of array communication.In order to fully reflect the natural spatial resources of array visible light communication and solve the problem of serious lack of channel matrix,this paper proposes a spherical distribution method of array,which optimizes the rank of space equivalent channel matrix and constructs the full rank matrix.The simulation results show that the array structure can effectively improve the rank of the channel matrix,and the decorrelation performance of the spherical distribution is better than the plane distribution which normal vector perpendicular to the receiving plane.3.Aiming at the problem that the interference signal ratio is relatively large,a new method of array multiplexing is proposed by tilting the vector direction of the array element to achieve the maximum interference signal ratio.This paper establishes a channel model of the array of visible light communication element vector tilt,and presents a method of channel decorrelation about the element vector tilting based on the analysis of the relationship between the channel correlation and the vector direction of the array element.That is,to minimize the maximum interference signal ratio,this paper optimizes the normal vector tilt angle,and structures a sparse symmetrical channel matrix.For the 2×2 VLC-MIMO system,this paper deduces the best tilt angle of the element vector;For the 9×9 and 16×16 VLC-MIMO systems,this paper simulates the best tilt angle of the element vector.The simulation results show that the optimal tilt angle value can improve the angle multiplexing gain and improve the communication performance,regardless of the theoretical derivation of the small array and the optimized simulation of the large array.4.Aiming at the efficient transmission of array communication in the relevant channel,this paper proposes a power allocation method based on the joint design of the transmitter and receiver.It is difficult to make the maximum interference signal ratio equal to zero by the tilting of the array element vector.So according to the photoelectric coordination,this paper presents a joint processing method based on power allocation and normal vector tilt to further improve communication performance.Basis on the tilting of the array element vector,two kinds of power distribution methods are proposed according to the interference signal ratio which is received by PDs,such as for the transmitter side of the system,this paper distributes the power of LEDs,and for the system receiver,with the PD on the light of the monochromatic sensitivity of different,this paper distributes the color of LEDs.The simulation results show that the performance gain is about 9~11dB through the transmitter power distribution method.The gain is 3~6dB through the equivalent receiver power allocation method.5.This paper establishes the non-line-of-sight link channel model of indoor array VLC,analyzes the element vector tilt technique and the corresponding channel decorrelation performance under non-line-of-sight(NLOS)link.According to the typical application scenario of indoor visible light communication,this paper establishes the NLOS link channel model of visible light communication.On this basis,this paper studies the decorrelation performance of element vector tilting technique when considering LOS link and NLOS link.The simulation results show that the communication system with LOS link and NLOS link has better communication performance than the system with LOS link,and the vector tilt technique can effectively reduce the channel correlation about LOS link and NLOS link.