Visible light communication system based on spread spectrum technology for intelligent transportation

In recent years, with the rapid development of the solid state Light emitting diodes (LED's) material, visible light communication has vast applications in transportation system. Generally, LED visible light communication refers to the communication technology which utilizes LED as a signal transmitter, the air as a transmission medium, and the photodiode as a signal receiving component. Visible light communication based on LED light source has been widespread concerned in intelligent transportation system (ITS). In particular, it is used to solve the communication problems between traffic lights and vehicles. However, signal source switching always puzzles the application of visible light communication based on LED in ITS. If signal source switching is not solved effectively, it will result in the interruption of information transmission. The paper proposes a visible light communication system using spread spectrum technology and pulse position modulation. When the vehicle is at the crossroads, the receiver on the vehicle receives signals from the four LED traffic lights at the same time. During the movement of the vehicle, the peak value of the four signals received by the receiver is constantly changing. The receiver detects the relevant peaks from the four traffic light signals and communicates with the traffic lights which have the maximum correlation peak. The problem of signal source switching is solved effectively. The experimental results show that the proposed system can achieve seamless switching between four-way LED traffic lights at the crossing, and the bit error rate of the system is 10(-4)-10(-7).