# Visible Light Communication: A System Perspective--Overview and Challenges
## 3 Applications
### Intelligent Transport System (ITS)  
Nearly 1.2 million people die in a traffic-related incident every year, and an estimated 50 million get injured [39]. Researchers have shown that most of the incidents are due to the slow response and inability of automobile drivers to take the right action at the right time [40]. In ITS, vehicle to vehicle (V2V) and infrastructure to vehicle (I2V) communication ensures the safety of people, traffic flow and comfort of drivers as shown in Figure 1. ITS relies on reliable, robust and secure communication among vehicle and infrastructure (traffic lights, billboards). VLC is proposed for ITS communication to complement or replace the existing crowded RF-based communication [11; 12]. All vehicles are equipped with head and tail lights that can be used for transmitting information. Traffic lights or billboards can also be used for sharing useful information about the road, traffic and weather conditions. These lighting sources can also be used for providing data connectivity to users and IoE entitites. [PERSON] et al. have discussed challenges facing VLC in the context of vehicular communication (VC) [41]. Increasing communication range, enhancing mobility and data rates are the main requirements for VC. The accomplishment of these objectives depends on the ability of communication channels to be resistant to parasitic light (PL). The outdoor channels are exposed to different kinds of PLs. It is observed that VLCs distance measuring and localisation capabilities could be beneficial in VC applications. Further, it is suggested that the development of heterogeneous systems consisting of VLC and dedicated short-range communication (DSRC) (or any other RF-based scheme) could lead to a reliable system for VCs as each of these technologies can make up for each other deficiencies. In this regard, a survey of VLC concerning 5 GHz DSRC in a hybrid arrangement is conducted. It is concluded that VLC systems aimed at VCs can be improved by exploring and integrating new technologies which include but are not limited to software-defined architecture, resource sharing, reconfigurable computing and integration of new materials. [PERSON] et al. have developed a hybrid 802.11p and VLC secure autonomous platoon system [42]. The autonomous platoon uses RF based 802.11p and consists of a platoon leader that controls other members to adjust the speeds stably. A 802.11p and VLC hybrid vehicular platoon communication protocol, named as SP-VLC is proposed. This protocol is aimed at addressing security vulnerabilities due to the exclusive use of RF communication. A simulation platform for the vehicle mobility and vehicle platoon managementis is developed. SP-VLC is evaluated under different security vulnerability scenarios. The simulation results validated the observations made in [41] that RF-VLC heterogeneous systems can provide many advantages over the RF only system. [PERSON] et al. have proposed to integrate LED-based road side units (RSU) into the existing ITS infrastructure [43]. The RSUs are used to broadcast information in infrastructure to vehicle (I2V) mode using VLC concepts. A robust modulation technique based on a direct sequence spread spectrum (DSSS) and sequence inverse keying (SIK) is employed to minimise the effect of noise sources. The amount of data received by a car passing by RSU is considered as a performance metric. The experimental setup involves a movable receiver and a stationary emitter both separated by a distance of 1.5 m. Results show that packet error rate (PER) degrades linearly with distance during daylight while at night the packet error varies due to the local nature of artificial light. In [44] performance evaluation of VLC based V2V systems has been conducted. For performance evaluation, a typical V2V VLC scenario is considered with left and right headlamps emitting light. The reflected rays are considered to have both line of sight (LOS) and non-line of sight (LOS) components with the Lambertian profile.