Research On Demodulation Algorithm Of Optical Camera Communication In Rolling Shutter Exposure Mode

In recent years,Optical Camera Communications(OCC)has received widespread attention due to the high penetration rate and low cost of its receiving equipment.OCC regards the LED light source as the transmitting end and the image sensor as the receiving end.The demodulation algorithm based on image processing is the basic problem of the OCC communication system.At present,OCC is limited by the frame rate of the image sensor at the receiving end,resulting in a very low communication rate.Rolling shutter exposure at the receiving end is one of the ways to increase the communication rate.Rolling shutter exposure at the receiving end is one of the ways to increase the communication rate.The light source appears as a strip of light and dark on the image.As the communication distance increases,the problem of internal interference between strips will occur,resulting in unclear boundaries between light and dark strips and an increase in bit error rate.Therefore,how to propose a demodulation algorithm against inter-band interference is a key issue to be solved in the OCC communication system.In this paper,in order to increase the transmission distance,we propose the efficient thresholding method which transforms partial mean gray values of per column nonlinearly to increase the contrast between light and dark bands.In addition,this method takes the frame image of the camera as the basic unit to adjust the threshold for the environment in which each frame of the image is located.Experimental results show that this method is better than the polynomial regression.Moreover,we perform the error correction of the block sequence number(BSN)by using its continuity to specify the legal BSNs and the illegal BSNs.In addition,we adjust the exposure time and sensitivity of the image sensor through Android programming,so that the communication distance and communication speed have been improved to a certain extent,and the problem of light source positioning and multi-light source is put forward.In 2011,the Institute of Electrical and Electronics Engineers(IEEE)released the IEEE802.15.7 standard,which proposed four uplink random access mechanisms for Visible Light Communication(VLC).Among them,the slotted carrier sense multiple access with collision avoidance(CSMA/CA)is the most popular way.However,due to the direct light characteristics,it is difficult for the terminal to detect the presence of other terminals,making the problem of hidden terminals particularly serious.The performance of CSMA/CA depends to a large extent on the accuracy of carrier sensing.Therefore,the hidden terminal problem cannot be ignored.In this article,in order to solve the problem of hidden terminals,this article proposes a VLC-WLAN network and designs an OCC-based ALOHA random access mechanism(OCC-ALOHA).This mechanism uses the OCC link in the uplink and uses the spatial resolution of the image sensor to enable the wireless access point(AP)to obtain multi-packet reception(MPR).The VLC link is used in the downlink for high-speed data transmission.The mechanism first uses the Spot Estimation(SE)algorithm to estimate the number of terminals,the distance between the terminal and the AP,and the incident angle of the terminal LED light source.Based on the above information,the Double Iteration(DI)algorithm is implemented to maximize the throughput of the system while ensuring the fairness of the terminal.Experimental results show that this method is better than CSMA/CA with hidden terminals.