# Outdoor Visible Light Communication in Intelligent Transportation Systems: Impact of Snow and Rain
## 1 Introduction  
The intelligent transport system (ITS) was motivated by the need to reduce traffic overcrowding and to provide better user experience through mobility and location-specific services. In addition, data transmission, real-time monitoring, and data-mining technologies can be combined to ensure effective traffic and software exchange. In ITS, visible light communication (VLC) technology is preferred over all other optical wireless systems, mainly because it is cost-effective and there is no need for \"licensing\" or new infrastructure. It can be used for communication due its wide range, and is environmentally friendly [1; 2; 3]. VLC was introduced for ITS interaction to complement and commute the present radio frequency (RF) communication by solving the saturation problem in its band, considering each light source as a free access point [4]. In the meantime, the light-emitting diodes (LEDs) that have been widely deployed in traffic lights can be used as VLC transmitters because they are a possible energy-saving light source, with long life, small size, and low power consumption. Therefore, LEDs are used on different occasions, such as for traffic lights and street lighting that can be used for communication, so that large-scale power can be employed effectively and that could not be used for radio or infrared contact [4; 5; 6]. Most VLC systems depend on the Line of Sight (LoS) transmission. Nevertheless, the spread of LoS cannot always be guaranteed, particularly in the outdoor environment, which is influenced by the spread disability due to adverse weather conditions and is considered to be a challenge for theVLC network. In general, scattering due to atmospheric aerosols/hydrometers such as snow, rain, fog, or dust can cause a significant extinction of the optical signal, resulting in system outage [7]. [PERSON] et al. analyzed the outage and BER performance of the vehicular VLC under rain and fog [8]. [PERSON] and [PERSON] studied how sensors in automated vehicles work in rain and fog to identify measurements errors [9]. For snow attenuation, [PERSON] has studied optical wireless link features such as signal-to-noise ratio (SNR), data rate, and receiver signal power for different snow rates [10]. [PERSON] investigated a free space optics link at different wavelengths under different weather conditions to acquire a minimum bit error rate (BER) [11]. Most recent work, as in Refs. [8; 9; 10; 11], focused on the visible light region beginning from red wavelength and higher or near-infrared regions, and then testing it on a free space application. Still, few works have been done on outdoor visible light applications under different weather conditions using a different wavelength of LED, especially the green wavelength. In this paper, we present a simple analytical model to fully study the impact of rain and snow attenuation on the outdoor VLC communication channel for 505 nm wavelength transmission. The use of a non-imaging concentrator coupled with a single photodetector is a cost-effective receiver in order to increase the overall performance of the system. The rain attenuation predicted by three different models (Marshall, France, and Japan) is studied, while snow attenuation caused by two different forms such as wet and dry is tested. The performance is studied for a two-lane road. The attenuation effect on system parameters such as maximum SNR, optical power received, BER, and maximum coverage area is investigated under different modulation techniques such as ON-OFF Keying (OOK), Subcarrier Binary Phase-Shift Keying (SC-BPSK), L-Pulse Position Modulation (L-PPM), and Inverse L-Pulse Position Modulation (I-LPPM). Finally, the amount of received information is investigated for two types of modulation schemes: 16 PPM and I-16 PPM. The remainder of this paper is organized as follows. Section 2 presents the system model and numerical analysis of the proposed system, including all equations used to evaluate the system performance. The simulation results are displayed and discussed in Section 3.