Research And Implementation Of Signal Equalization Algorithms Based On Visible Light Channel

With the development of information technology,spectrum resources are constantly being occupied,and how to better utilize spectrum resources has become a hot issue recently,which has aroused many concerns.Although the development of microwave technology can improve the utilization rate of spectrum,the use in hospitals,airports and other places will be limited.The visible light communication uses indoor lighting equipment instead of the WLAN or the base station to transmit signals,uses white light as the medium for illumination and information transmission.While realizing illumination,information transmission can be performed,and the electromagnetic interference problem can be well solved.However,in the process of data transmission,due to diffuse reflection and multipath transmission,severe intersymbol interference(ISI)will occur,and the signal will cause severe distortion.In response to this problem,this paper has made improvements in the signal receiving terminal,and the improvement method is as follows.Firstly,based on the existing FFE and DFE equalizer structure,combining the advantages of two different equalizers,optimizing their combined structural parameters,and adding the MAP algorithm on this basis,so that not only can the information system have a real-time response,but also can restore the received signal to the transmitted initial signal with a small error probability.Secondly,the error function of the traditional equalization algorithm does not have symmetry,so that the same equalization effect can not be obtained to the points with the same distance of the output signal,which will make the convergence speed of the algorithm slow and the mean square error increases,so this paper proposes a hyperbolic tangent function improves the defect of the traditional error function and speeds up the convergence without changing the mean square error.Then,based on the existing iterative algorithm,there are problems such as slow convergence speed and large steady-state error.In this paper,we propose a FFE-DFE-MAP equalization structure and an improved hyperbolic tangent error function,and based on this,the fixed step size of the CMA algorithm is improved to the adaptive tangent function step size.The optimal value of the two parameter adjustment factors computed by MATLAB of the step function optimizes the convergence performance of the CMA algorithm.According to the above improvements,compare the convergence speed and residual error of the proposed algorithm and the other two domestically proposed algorithms.Through the calculation of MATLAB,the calculation results show that convergence performance of the proposed algorithm is proved.The convergence speed of the algorithm is increased by 53.6% and the steady-state error is reduced by about 6dB compared with the traditional CMA algorithm.And the convergence speed of the algorithm is 33.3% and 12% higher than the domestic CMA algorithm and the foreign CMA algorithm respectively,and the steady state of the algorithms is reduced by about 5dB and about 3dB.Finally,the algorithm is transplanted into the ARM hardware signal processing module to realize visible light communication.The received signal is equalized at the receiving terminal using the ARM signal processing module.It can be seen from the experimental results that the intersymbol interference in visible light communication is improved after equalization,which indicates that the equalization algorithm proposed in this paper can play a good role in visible light communication.