Demodulation Algorithm And MAC Random Access Mechanism For Optical Camera Communications

In recent years,optical camera communications(OCC)has become one of the research hotspots in the field of visible light communications(VLC)due to its high popularity of communication devices and the natural integration with some new technologies such as Internet of Things,Internet of Vehicle.The IEEE 802.15.7r1 protocol provides a global standard for OCC and promotes its standardization development in the fields of Internet of Things,Internet of Vehicle,underwater communications and so on.OCC uses a camera based receiver to capture the brightness states of the LED light source in the form of images.Therefore,the demodulation algorithm based on image processing becomes a basic problem in the study of the physical layer of OCC.At present,related researches on OCC are carried out in static communication scenarios,that is,the transmitter and the receiver of the communication system are required to be in static at the same time.The reason is that the existing demodulation methods cannot support the mobility of the terminal.Therefore,how to propose a demodulation method with movement robustness to apply OCC to mobile communication scenarios is a key problem to be solved urgently.In addition,in wireless optical network link layer,considering the narrow beam and directional transmission of the light in VLC,the mode of data transmission should mainly be line-of-sight transmission.It is difficult for terminals to detect signals transmitted by other terminals by sensing,and the hidden terminals problem is more serious.Therefore,CSMA random access mechanism based on carrier sensing is not suitable for VLC.Scholars recommend that ALOHA-type random access mechanism should be preferred in VLC systems,but the collision probability of ALOHA-type random access mechanism will increase significantly with the increase of the number of terminals.Therefore,how to combine OCC with traditional VLC technology to alleviate access collision and design a fair and efficient random access strategy should be the key to the research of wireless optical network link layer.Firstly,a block matching demodulation(BMD)algorithm with movement robustness is proposed.Inspired by the idea of motion estimation in video compression coding,BMD algorithm uses template matching to track the imaging position of the communication lightsource in real time in the image captured by receiver.In this paper,a new data frame structure is designed by using the fast time-varying characteristic of the communication light source to assist BMD algorithm to immunize the interference of non-communication light source,and to realize the accurate recognition of the communication light source imaging.In addition,this paper combines BMD algorithm with Manchester decoding to achieve error detection and correction without increasing the encoding overhead of the communication system,and further improves the reliability of OCC system in mobile scenarios.A VLC wireless local area network(VLC WLAN)based on image sensor is proposed in this paper.By utilizing the spatial resolution of image sensor in OCC link,the network enables the multi-packet reception(MPR)capability of AP,thus alleviating the access collision problem;And the network realizes high-speed data transmission through VLC link.In addition,this paper designs an OCC-ALOHA random access mechanism.The mechanism estimates the number of active terminals,the distances between AP and terminals,and the emission angle of terminal LED light sources by using spot-estimation algorithm.On the basis of the above estimation information,the terminal access probability optimization algorithm is used to calculate the access probability of each terminal in order to achieve the dual objective optimization of access fairness and system throughput.