| Popis: |
When a car enters a corner with over speed, it rises the accident risk higher. To warn the risk and urging the caution to drivers, many of the accident-prone corners have warning rights. The driver can decelerate the car smoothly and pass through the corner safety by those devices. However, appropriate speed for each corner is different by curvature of the corner and characteristics of the vehicle. The driver has to suppose the safe speed for every corner only by experience, usually. Of course too much slow causes traffic jam. Especially at the first road in the first place for the driver, it is difficult to suppose the curvatures of the corners. Then, we propose a visible light communication system so that the warning lights in the corner send appropriate warning information. Visible light communication transmits a signal by blinking the light. One of the characteristics of visible light communication is that it can use existing lighting equipment as a transmitter. In our system, we can distribute the warning information to the driver using the visible light communication. Though the curvature(R:radious) of the corner does not change, the speed of each vehicle to approach the corner always to different. Focusing the distance from the corner to the car, we consider a communication system to send different kind of information according to that distance. If the distance is enough long, the driver has a plenty of time to decelerate the vehicle. The more the distance becomes short, the more the driver is required rapid deceleration. Therefore, to distribute the appropriate warning information to the driver, dividing the distance from the corner into some areas, we make the system to send different information in each area. Generally in communication system, modulation primarily changes the amplitude, phase or frequency. In visible light communication, change of the amplitude changes the brightness, which causes flickering that burdens the drivers. Therefore we cannot use amplitude based modulation. Next we consider the varying the phase. Unfortunately, it is difficult for the receiver using photodiode or phototransistor to read the difference of the phase of the signals, because the frequency of the light is very high in visible light communication. Then we employ 'symbol length' with the Pulse Position Modulation (PPM).In our method, brightness does not change when the symbol length is changed. We investigate the system performance by changing the communication speed. Short symbol length in high frequency is sensitive and vulnerable to noise, instead of low frequency with strong against noise. Using this characteristic of symbol length modulation, different information in each distance can be delivered by changing the frequency. As conclusions, we propose awarning system for over speed at the corner using visible light based road-to-vehicle communication. The installed light in the wall deliver the information using visible light communication. In our system, lighting device delivers different information according to the distance from the corner to the car.In our proposing method, brightness does not change by using the PPM and symbol length modulation. |
