Capacity Analysis And Transceiver Design For Visible Light Communication Systems

VLC is one communication technology which utilizes visible light with spectrum 400-800 THZ to transmit information;Due to the advantages including no spectrum license,no electromagnetic radiation to the human body,energy saving for the integration of illumination and communication,and the fulfillment of communication requirements in electromagnetically constrained environments,VLC is considered as an important supplement to traditional wireless coverage,and has attracted great attention in both academia and industry.In this dissertation,the problems of capacity analysis and transceiver design are investigated for VLC systems.The main contributions are listed below.Firstly,the capacity problem is investigated for SISO-VLC systems with signal-dependent additive shot noise in both the absence and presence of average optical power constraint.The main work includes: 1)In the case with/without average optical power constraint,the capacity problem is written as a functional optimization problem,which is proven to be a convex functional optimization problem with one unique solution;2)In the case with/without average optical power constraint,an necessary and sufficient condition is given for the input probability density function achieving capacity;3)In the case with/without average optical power constraint,based on the optimal condition,it is proved that the input distribution achieving capacity must be a discrete distribution;4)In the case with/without average optical power constraint,the equations are derived for the optimal discrete input distribution achieving capacity.Secondly,the basis and constellation design problems are investigated for SISO-VLC systems employing two-dimensional modulation.The main work includes: 1)The mathematical representations of the VLC signal constraints and corresponding signal space are derived for SISO-VLC systems employing two-dimensional modulation under given modulation basis functions;2)Assuming that one basis function represents the direct current component,it is proven that the other basis function maximizing the area of signal space is a two-value function with the two values being opposite and each occupying half of the symbol period.3)The minimization of SER is transformed into the maximization of minimum Euclidean distance,based on which two-dimensional constellations are designed;The original non-convex constellation optimization problem is iteratively solved by transforming it into a linear programming with the first-order Taylor approximation,which is proven convergent to the KKT points of original non-convex optimization problem.Thirdly,improved receiver designs are investigated for PAM-DMT and Flip-OFDM systems.The main work includes: 1)The relationship between the real/imaginary parts of received PAM-DMT signals and transmitted data is derived by utilizing the characteristics of PAM-DMT transmitter and following the signal flow;Based on the derived relationship between the transmitted and received signals,an iterative receiver is proposed for PAM-DMT by jointly utilizing the real and imaginary parts of received signals;2)The relationship between the received signals in the positive/negative subframes of Flip-OFDM and transmitted data is derived by utilizing the characteristics of Flip-OFDM transmitter and following the signal flow;Based on the derived relationship between the transmitted and received signals,an iterative receiver is proposed for Flip-OFDM by jointly utilizing the received signals in the positive and negative subframes.Fourthly,transceiver design is investigated for MIMO-VLC systems employing integerforcing receiver.The main work includes: 1)A necessary and sufficient condition is derived for the integer matrix in MIMO-VLC systems employing pulse amplitude modulation and integerforcing receiver;2)An optimization problem with respect to the DC bias,precoding matrix,equalization matrix and integer matrix is formulated by maximizing the sum MSE in integerforcing receiver under the constraints of VLC signal and integer matrix,and then simplified to an optimization problem with respect to only the precoding matrix and integer matrix based on the corresponding characteristics and optimal conditions;3)The simplified optimization problem is decomposed into two subproblems,of which the first one is the optimization problem with respect to the precoding matrix given integer matrix,and the second one is the optimization problem with respect to the integer matrix given precoding matrix;4)Two feasible direction methods,namely the conditional gradient method and projected gradient method are adopted to solve the first subproblem;a heuristic algorithm based on lattice reduction and sphere decoding is proposed to solve the second subproblem;A suboptimal solution of the original optimization problem is obtained by iteratively solving the first and second subproblems.