Research On Precoding And Resource Allocation Of Visible Light Communication System

With huge bandwidth and system capacity,VLC can provide high-rate short-distance wireless communications without interfering with existing mobile networks,and is an ideal complement to RF systems.In this thesis,the precoding for the downlink of multi-user MISO VLC system and the resource allocation of multi-color LED based VLC system are studied,and the main contributions are as follows:(1)The zero-forcing precoding for maximizing the achievable rate of multiuser MISO VLC system is studied.For the downlink of indoor MISO VLC system,a problem of maximizing the sum rate is proposed to optimize the precoding matrix where the zero-forcing precoding is applied while considering per-LED optical power constraints.The rate-maximization problem is a non-convex problem.To handle the non-convexity,the non-convex constraint is firstly approximated to a simple form by applying the Cauchy-Schwarz inequality,then an approximate problem of the original problem is obtained.Next,an iterative method which named successive parameter convex approximation is used to solve the approximate problem,and the iterative algorithm finally converges to the local optimal solution.In addition,two simplified schemes for the rate maximization problem are studied.(2)The integer-forcing precoding for minimizing MSE of the multiuser MISO VLC system is studied.For indoor multi-user MISO VLC downlink system,a problem of minimizing the sum MSE is proposed to optimize the transmit precoding matrix and IF integer matrix while considering per-LED optical power constraints.The MSE-minimization problem is a non-convex problem.To handle the non-convexity,the alternating optimization technique is applied and an iterative algorithm comprised of two sub-problems is proposed.The two sub-problems are about the optimizations of precoding matrix and IF integer matrix respectively.In each iteration,a solution of transmit precoding matrix is firstly derived for given IF integer matrix.Next,the IF integer matrix is derived based on previously obtained transmit precoding matrix by a greedy method.The proposed algorithm finally converges to a local optimal solution,hence a suboptimal precoding matrix and a suboptimal IF integer matrix are obtained.(3)The optimal resource allocation problem for multi-color LED based VLC system which serving multiple users is studied.The rate maximization problem and the average optical power minimization problem are proposed under the power constraints and chromaticity constraints,and the corresponding optimization variables are the DC bias,average luminous flux,and modulation symbol interval parameters of the system.The two optimization problems are equivalent to corresponding convex problems,hence any existing algorithms for solving convex problems can be applied to solve these two problems,and the global optimal solutions are obtained.(4)The optimal resource allocation problem for point-to-point multi-color LED based VLC system where the SVD precoding scheme is employed is studied.The sum-rate maximization problems and energy efficiency maximization problems are proposed under the power constraints and chromaticity constraints in order to optimize the DC bias,average luminous flux and modulation symbol interval parameters of the multi-color LED based VLC system.It can be seen that the rate maximization problem is a convex problem,hence any existing optimization algorithms for solving convex problems can be used to obtain the optimal solution.The energy efficiency maximization problem is a fractional programming problem,hence an iterative algorithm based on the Dinkelbach method is proposed and it can converge to the local optimal solution.