Abstract
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.
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