| The increasing demand for data traffic usage and the shortage of Radio Frequency（RF）spectrum resources have forced the demand for new spectrum other than RF.With the widespread use of smartphones based on embedded Complementary Metal Oxide Semiconductor（CMOS）Image sensors（IS）,Visible Light Communication（VLC）based on image sensor,namely Optical Camera Communication（OCC）,is regarded as a potential wireless communication technology to realize the Internet of everything.Although OCC has great development potential,the relevant research on OCC system is not mature enough.Many researches are still at the level of computer simulation,lack of experimental platform support and research on communication performance in different environments.The traditional image processing algorithm,which is easily affected by the binarization threshold and cannot adapt to the complex environment background.Compared to VLC systems based on photodiode（PD）,OCC systems have a lower transmission rate and use complex image processing algorithms to improve the overall system time complexity.The decoding algorithm of target Light Emitting Diode（LED）array for OCC system was studied under different environments.The main work and contribution of this paper are as follows:（1）Analysis and optimization of Gradient-Harris decoding algorithm in multiple environmentsIn order to improve the decoding rate of the OCC system receiver,the calculation amount of the traditional Hough circle is reduced from three-dimensional space to two-dimensional space（Gradient algorithm）,which is used to detect the target LED array.In order to overcome the disadvantage of the traditional Hough circle algorithm,which is easily affected by binarized threshold during state recognition,the Gradient-Harris algorithm is proposed by combining the Gradient algorithm and Harris detection algorithm to identify the state of the target LED array by using the location parameter information of the target.To improve the decoding rate and the robustness of the system in a complex environment,the standard correlation coefficient matching algorithm is used to optimize the Gradient-Harris algorithm.The experimental results show that the bit error rate of the optimized Gradient-Harris decoding algorithm is 0 and the average decoding rate increases from75.89bit/s to 142.36bit/s under the indoor environment without interference light source.In the indoor environment with interference light source,the bit error rate of the optimized Gradient-Harris decoding algorithm decreases from 1.88×10-3to2.89×10-4,and the average decoding rate increases from 74.27bit/s to 144.39bit/s.In the outdoor road environment at night,the bit error rate of the optimized Gradient-Harris decoding algorithm is 2.29×10-4,and the average decoding rate is148.14bit/s.The bit error rate of the optimized Gradient-Harris decoding algorithm is4.60×10-3and the average decoding rate is 143.74bit/s in the outdoor strong daylight rooftop environment.（2）Analysis and optimization of decoding algorithm based on image enhancementIn view of the dramatic increase of interference factors and the sudden increase of bit error rate in the outdoor strong daylight rooftop environment,a Gradient-Harris decoding algorithm based on image enhancement is proposed,and three image enhancement algorithms including gamma transform,histogram equalization and linear gray transform are realized and analyzed.A piecewise linear gray transform with specific parameters is designed to optimize the linear gray transform according to the imaging effect of the camera at the receiving end of OCC system under strong sunlight.The above four algorithms were used to enhance the images extracted after ROI,and then the Gradient-Harris algorithm was used to decode the images,the decoding rate and bit error rate after the four image enhancement algorithms were calculated.The experimental results show that the bit error rate decreases from 4.60×10-3to4.38×10-4when the image is enhanced by the segmented linear gray transform of specific parameters and then decoded under the outdoor strong sunlight roof environment. |
PDF Full Text Request