A Survey on the Roadmap to Mandate on Board Connectivity and Enable V2V-Based Vehicular Sensor Networks <s> Visible Light Communication (VLC) <s> The paradigm of vehicular visible light network (VVLN) is introduced, highlighting its peculiarities, and discussing the present state of the art focusing on standardization and real experimentations.The limits of visible light communication (VLC) for pure VVLNs are discussed and its potentiality when used as complementary wireless technology is highlighted.An algorithm (called congestion-adaptive VLC-DSRC) is proposed to jointly manage VLC and dedicated short range communications (DSRC) in heterogeneous vehicular networks.Example results of VLC added to DSRC are shown focusing on the example application of crowd sensing vehicular networks (CSVNs) through simulations in realistic urban scenarios. The paradigm of connected vehicles is moving from research to implementation, thus enabling new applications that start from safety improvement and widen to the so called Internet of vehicles (IoV). The candidate enabling technologies in the radio frequency (RF) bands are cellular and short range technologies. However, the limited bandwidth shared among several applications pushes researchers to look at new technological solutions. To this end, an option is provided by visible light communication (VLC). Based on the use of the light emission diodes (LEDs) that are already available on the majority of vehicles, VLC would enable short range communication in large, unlicensed, and uncongested bands with limited costs. In this work we first highlight the main properties of VLC in vehicular networks and revise the state of the art focusing on both the IEEEź802.15.7 standard and on the performance demonstrated by field tests that have been conducted worldwide. Then, we discuss the limitations of using VLC for pure vehicular visible light networks (VVLNs) and its application as complementary technology, to be implemented with other wireless standards in future heterogeneous vehicular networks. Finally, we show numerical results provided by simulations in a realistic urban scenario focusing, as a case study, on the crowd sensing vehicular network application with VLC added to short range IEEEź802.11p technology. Results demonstrate that the addition of VLC improves the performance of a conventional vehicular network based only on IEEEź802.11p. <s> BIB001 </s> A Survey on the Roadmap to Mandate on Board Connectivity and Enable V2V-Based Vehicular Sensor Networks <s> Visible Light Communication (VLC) <s> Direct connectivity between vehicles will let a variety of new applications become a reality, from safety to traffic management and infotainment. Different wireless access technologies can enable this kind of connections, from mobile-fi IEEE 802.11p in the US and ETSI G5 in Europe, to the more recent 3GPP long term evolution (LTE) for vehicle-to-vehicle (V2V) communications. To integrate the capabilities and performance of these radio access technologies, light emitting diodes (LEDs) operating in the front and rear vehicles' lights, can introduce a further degree of connectivity through the so called visible light communication (VLC), by setting up direct links between vehicles in visibility and between vehicles and the road side (such as traffic lights and variable message panels). This paper investigates the performance of vehicular visible light networks (VVLNs) in terms of message delivery rate when full-duplex (FD) capabilities are exploited. Specifically, instead of considering carrier sensing multiple access with collision avoidance (CSMA/CA) as foreseen by the IEEE 802.15.7 standard for VLC, we here propose a CSMA with collision detection (CSMA/CD) protocol exploiting the reverse link made available by the concurrent use of LEDs as transmitters and photodiodes as receivers for an immediate feedback during decoding. Results show an increase of up to 10% in the delivered data thanks to FD in realistic urban scenarios and give guidelines to network designers. <s> BIB002 </s> A Survey on the Roadmap to Mandate on Board Connectivity and Enable V2V-Based Vehicular Sensor Networks <s> Visible Light Communication (VLC) <s> As the demand for wireless communication technologies is exponentially increasing, using the visible light electromagnetic spectral region is a logical option. This article provides a general analysis of the IEEE 802.15.7 standard for optical communications using visible light, focusing on the PHY I, intended for outdoor applications. Moreover, the article discusses how the standard's specifications apply to visible light communication use in vehicular networking applications. The article concentrates on the standard's applicability in this domain, and points out the fact that it has not been widely accepted, as most of the VLC developers are focused on decreasing system complexity and implementation costs, rather than complying with the standard's requirements. Furthermore, the article points out the necessity of a novel vehicular applications VLC specific standard, which should focus on the requirements imposed in this specific area. <s> BIB003 </s> A Survey on the Roadmap to Mandate on Board Connectivity and Enable V2V-Based Vehicular Sensor Networks <s> Visible Light Communication (VLC) <s> Crowd sensing is a powerful tool to map and predict interests and events. In the future, it could be boosted by an increasing number of connected vehicles sharing information and intentions. This will be made available by on board wireless connected devices able to continuously communicate with other vehicles and with the environment. Among the enabling technologies, visible light communication (VLC) represents a low cost solution in the short term. In spite of the fact that vehicular communications cannot rely on the sole VLC due to the limitation provided by the light which allows communications in visibility only, VLC can however be considered to complement other wireless communication technologies which could be overloaded in dense scenarios. In this paper we evaluate the performance of VLC connected vehicles when urban crowd sensing is addressed and we compare the performance of sole vehicular visible light networks with that of VLC as a complementary technology of IEEE 802.11p. Results, obtained through a realistic simulation tool taking into account both the roadmap constraints and the technologies protocols, help to understand when VLC provides the major improvement in terms of delivered data varying the number and position of RSUs and the FOV of the receiver. <s> BIB004
VLC allows high data rate transmission at the same time as illumination, by exploiting the same main principles of Bell's photophone transmissions dated more than 100 years ago. It is, in fact, sufficient to quickly switch on and off the light emitting diode (LED) to transmit a wide bandwidth signal invisible to the human eye and completely safe for the human body, by exploiting the wide and free optical spectrum. VLC is, thus, naturally suited to broadcast messages. Vehicles are already equipped with LED lights that could be easily exploited for V2V communications without interfering with electromagnetic devices and allowing a high reuse factors and lower interference from neighbors thanks to the limited penetration capabilities of light BIB004 . Besides these advantages, it has to be remarked that VLC is susceptible to ambient light and weather conditions, covers limited distances and does not cross obstacles BIB002 BIB001 . The increasing interest in this kind of communication is also demonstrated by the development of the IEEE 802.15.7 standard, which defines the PHY and MAC layers for the visible light spectrum and allows for supporting audio and video services also in mobile visible links  . At the PHY layer, three are the available operating modes which differ in the adopted modulation and coding scheme   , allowing data rate from 11.67 to 96 Mb/s. At the MAC layer, the IEEE 802.15.7 standard foresees the use of CSMA/CA: each node transmits only if the medium is sensed as idle after a random backoff interval time; then, the message is considered correctly received only upon the reception of an acknowledgment at the transmitter. A revision of the standard, called IEEE 802.15.7r1, is foreseen to better address vehicular communications as a VLC use case. In this case, the standard considers the requirements of vehicular communications and aims to enhance mobility, data rates, robustness and the networking protocols BIB003 .