Research And Implementation Of Channel Estimation Algorithm In Visible Light Communication DCO-OFDM System

Visible light communication has the advantages of lighting and high-speed data communication at the same time,which has become one of the hotspots in wireless communication field in recent years.DCO-OFDM is the main modulation method for high-speed data transmission in visible light communication.Channel estimation of DCO-OFDM system is one of the key modules of receiver.In this paper,the channel estimation of DCO-OFDM system is studied.The main contents are as follows:Firstly,a pilot-based DFT channel estimation algorithm for DCO-OFDM visible light communication systems is studied.The accuracy of the DFT-based algorithm without virtual carriers is high,and it is improved to set the noise threshold threshold method to further improve the estimation accuracy.For the DFT-based algorithm with virtual carrier in the actual system,there are energy leakage problems,which are used to compensate the virtual edge of the channel value of the repeated edge value method,part of the sub-carrier replacement method and the optimal compensation DFT algorithm,also used the domain correction estimation algorithm is improved and the performance is improved,and the algorithm is simulated and analyzed.Secondly,ML channel estimation algorithm based on reliable decision feedback is improved.Based on the ML channel estimation algorithm of reliable decision feedback,the lower reliability of the BER signal is used as the quasi-pilots of the feedback,and the estimation accuracy is improved by the second estimation.However,the algorithm is unreliable at low SNRs for less performance improved.In this paper,we propose an improved ML channel estimation algorithm based on reliable decision feedback.In different SNR cases,different BER thresholds are set so that there is a certain number of quasi-pilots at low SNRs,which can be improved the estimated performance at low SNRs.Thirdly,ROMP sparse channel estimation algorithm based on compressed sensing is improved.Simple greedy iterative algorithm is studied,including OMP algorithm and ROMP algorithm.OMP algorithm is simple and accurate,and ROMP algorithm in the regularization process exists in the possibility of selecting the wrong atom,proposed an improved algorithm for this problem.The improved algorithm improves the regularization process,reduces regularization coefficient and chooses the atomic group with the highest average energy rather than chooses the largest sum of energy to reduce the possibility of selecting the wrong atom,and carries on the simulation and analysis.Lastly,the channel estimation module in the visible DCO-OFDM system is implemented in hardware using the Xilinx Kintex 7 series of FPGA development board.The design of the whole architecture of VLC system is introduced.The fixed point scheme of the channel estimation module is determined,and the performance difference between fixed-point and floating-point simulation is compared.The channel estimation module of the FPGA implementation process,including the sub modules(ROM matrix,multiply accumulator,FFT module),port signals and timing of key data are studied,and tested on the development board.