Research On Mac Protocol Of Visible Light Communication System And Terminal Software Implementation

Visible light communication (VLC) use a Light-Emitting Diode (LED) emitting a fast blinking signal to communication. VLC systrem has a lot of advandges such as wide range of applications, security, eye-safe, no electromagnetic interference and so on.Indoor VLC technology use LED devices for indoor lighting and data transmission. The key technologys of MAC protocol are conflict detection, random access mechanism and backoff algorithm. Existing solutions would cause many problems like unfair of nodes, low channel utilization and conflicts in high load. In this paper, we analysised the VLC system network performance based on markov chain model. The simulatition of indoor multi-terminal communication process is given to improve the random access mechanism. Methods have been given to reduce the conflicts between nodes, which provide a strong theoretical support for the realization of the VLC system.In view of the problem that low efficiency of existing light communication system between ships, and lacking of alternative scheme when radio communication was shut down, a long-distance optical communication system based on Embedded ARM platform is presented and demonstrated. The system is composed of two parts: LED/PD application terminal and its drive circuit. Terminal has a4-inch touch screen with interactive interface based on Android system. The performance of data transfer in our prototype shows up to50m range at the transmission rate of50kbps. This system is supposed to reach the distance of1km or higher in the coming months.This paper is based on the projects of "Key techniques of VLC system", to build all the modules in projects and optimize the algorithm combine the corresponding projects. And the main work and innovation points as below:1. The solutions of multi-terminal access system are proposed after analyzed the MAC protocol structure and function of VLC system. Power control is used to collision detective and balances the nodes. The indoor channel characteristics are analysied and we given out the design of the uplink and down link of VLC system.2. Network performance of VLC systerm is analysised using OPNET simulation system. Research shows that random access mechanism for VLC systems impact on throughput rate when network load change. In this paper we put forward a method with modify the parameters and improve backoff algorithm to optimize the network performance.3. A long distance visible light communication system between ships is designed and implemented in this paper. Morse code decoding method and the simple communication protocols are put forward. The terminal software with friendly interface based on android systerm is developed.