Experimental Demonstration of VLC-based Vehicle Communications under Atmospheric Conditions

Abstract

Visible light communication (VLC) is a wireless data transmission technology using existing luminance to transmit data. Generally, VLC is operated with light emitting diode (LED) as transmitter which gives inherent strong points such as low power consumption, a long lifetime and rapid blinking speed for data communication. So, LED is used not only as a lighting device, but also as a communication device. On the other hand, VLC possesses many advantages over conventional RF communications, such as safety for human body, highly secure and it have vast unregulated frequency spectrum. For these reason, VLC has been proposed to provide vehicle communication recently. In order to provide LED-based VLC for vehicle communication on outdoor conditions, this thesis addresses some of important issues outdoor VLC with experimental studies. Moreover, the thesis provides a fundamental analysis of the VLC system in outdoor weather condition with solutions. In the first study, sunlight with artificial light, which should be real priority weather condition for outdoor VLC system, is analyzed. In order to overcome this effect, filtering techniques with differential decision threshold (DDT) in the existing of sunlight and/or artificial light is presented. In the proposed system, optical filter is utilized for reducing effect of ambient light noise and sunlight. Color filter is employed for detecting a specific wavelength which include transmitted signal only at the receiver with DDT. Secondly, the thesis presents the effect of cloud on the intelligent transportation system (ITS) communication using VLC. For robust and reliable detection in the VLC-based I2V, the receiver structure of the proposed system is comprised of optical filter, color filter and Fresnel lens. We consider two primary atmospheric conditions in the highway I2V, i.e. sunlight and cloud effects. To alleviate these adverse effects, we propose an efficient and robust Zone Detection (ZD) and Adaptive Decision Threshold (ADT) method. The sunlight effect is reduced predominantly by the ZD, while the cloud effect is lessened significantly by the ADT. Thirdly, the thesis presents the effect of atmospheric turbulence particularly in rainy condition on the vehicle-to-vehicle (V2V) communication using VLC. The experiments for the V2V communication system was implemented with a modified fixed decision threshold (MFDT) scheme in the presence of rain drops. In the proposed study, a red LED representing the taillight of a vehicle is employed for transmitting signal and a photodiode is used to recover the transmitted the data using MFDT. It is demonstrated that the proposed V2V communication using VLC under the rainy condition is accurate and reliable with the help of MFDT. The last study in this thesis proposes V2V communication using VLC technology under fog conditions is presented. Fog is known as one of the most detrimental atmospheric conditions that cause outdoor optical wireless communications to be unreliable. The effect of the fog conditions is experimentally analyzed in the VLC based V2V system. Recognizing the least attenuation coefficient and a taillight color of a vehicle, a red light-emitting diode (LED) was employed in the experiment. In addition, a Fresnel lens and multiple photodiodes are utilized to efficiently counteract the impairment caused by fog. The experimental results demonstrate that the proposed VLC-based V2V system offers a reliable V2V data transmission over the fog-impaired optical channel with a relatively high signal-to-noise ratio (SNR), even under a heavy-fog condition.