Adaptive Transmission And System Scheme Improvement In DCO-OFDM Visible Light Communication System

Visible light communication technology has become one of the hotspots in the field of wireless communication in recent years because of many advantages.And OFDM is the basic method of modulation of high speed transmission in visible light communication.In this paper,the adaptive transmission and system scheme improvement of DCO-OFDM visible light communication system are studied.The main work is as follows:Firstly,the frequency domain LS channel estimation algorithm and the number of effective taps of channel impulse response are improved in DCO-OFDM indoor visible light communication system.Based on the channel estimation algorithm based on DFT,this paper compares some previous improved methods under the condition of existing virtual subcarriers:extrapolative method,iterative method and time-domain LS algorithm.In addition,an improved scheme of estimating the number of effective taps of channel impulse response in DCO-OFDM system is proposed.The improved scheme is applied to DCO-OFDM system with STO,which reduces the "platform effect" and improves the performance of MSE.Secondly,the adaptive modulation algorithm of DCO-OFDM visible light communication system is improved.Based on the principle of Water-Filling,combined with Greedy algorithm,an improved fixed threshold adaptive modulation algorithm is raised based on the principle of fully utilizing the power margin.In addition,the performance of the two adaptive schemes for subcarrier adaptation and sub-band adaptation are simulated and compared,and the optimal grouping strategy is given.Then,the nonlinear equations satisfying the optimal DC bias of the DCO-OFDM visible light communication system are deduced,and the numerical solution of the equation can be acquired by iterative method.Based on the AWGN channel condition and optical SNR,the expression of SNDR is given,and furthermore,the nonlinear equations satisfying the optimal DC bias of unilateral and symmetrical bilateral clipping are obtained.Furthermore,PSO-OFDM,an improved modulation scheme of DCO-OFDM,is proposed,which divides the DCO-OFDM signal polarity into two parts:positive and negative,and then transmits with two symbols respectively.It is proved that PSO-OFDM is better than DCO-OFDM in the terms of the SNDR performance and requirement of LED dynamic range.Finally,this paper introduces the design and implementation of the digital baseband hardware implementation scheme of the DCO-OFDM indoor visible optical communication system.The main contents is divided into 3 aspects:first,the overall system and parameters,the concrete block diagram of the hardware implementation;second,the algorithm of the receiving module including frame synchronization and AGC module,channel estimation and equalization module,phase compensation module and QAM soft demodulation module;third,fixed point scheme,key parameters of key IP core and key timing of each module.