| With the progress of the communication, novel techniques based on visible light become the researchful focus. Visible light communication based on white LED light transmitting in free space, which makes many scientists interested because of the advantages such as none electromagnetic radiation, green illumination, high safety to human being, uncovering wireless spectrum and high power. It also takes advantages of illumination and communication for the communication based white LED. In order to let multiple users communicate simultaneously, and to solve the problems of the high interference between users, a visible light communication system based on CDMA techniques is studied.In order to communicate simultaneously by multiple users while without interference each other, the visible light communication system based on the CDMA technique which is currently the main access technology for the third generation of mobile communication system is developed. The whole system consists of CDMA communication subsystem, visible light communication subsystem. The CDMA communication techniques and its advantages utilized in satellite communication, mobile communication and wireless local area network are introduced briefly. For the sake of improving stability and the ability for anti-interference, method based on compound spread spectrum code sequence with m-sequence and Walsh code is put forward and studied. For the visible light communication subsystem and the subsystem for signal generation, transmission and receiving, signal generator based on CPLD, white LED driver, receiver are implemented. In order to solve the signal synchronization, the protocol on the basis of the asynchronous serial communication protocol is utilized. Experiments for the researched visible light communication system show that information to local users can be decoded accurately from the received signal. The aim for 8 users communicate simultaneously without interference each other is reached successfully. |
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