## 2 Current Studies and Technologies for V2X Services
### Evolution of Vehicles Using V2X Services  
The study on the socio-economic benefits of cellular V2X [17] conducted by \"The Analysysys Mason\" [17] specifies four (4) case scenarios to study the evolution of vehicles either equipped with IEEE 802.11 or C-V2X technologies for deploying V2X services. These case scenarios are numbered from one (1) to four (4). Scenario one (1) is the case adoption of C-V2X and IEEE 802.11p in the absence of any government measures. The second scenario is the case all new vehicles to support ITS services using IEEE 802.11 p in 2020; the third scenario is the case in 2023 all new vehicles are equipped with LTE PC5. The fourth scenario is the case the Equitable 5.9 GHz use is adopted for V2X communications.  
Lessons learned from the study in [17] are described in Table 1, which summarizes case scenarios about V2X communications and relevant challenges. In the absence of any government regulations, V2V would use IEEE 802.11p or LTE-V2X PC5 [18]. This means that no-direct communication interoperability between IEEE 802.11p and PC5 exists. Therefore, V2V is possible via cellular LTE and vehicles without IEEE 802.11p or PC5 will use V2I and V2P via LTE-Uu of a smartphone brought in the vehicle. The case scenario 2 concerns all new vehicles that will use IEEE 802.11p in 2020 to support ITS services. Although vehicles without IEEE 802.11p would not communicate via V2V and V2I, vehicles equipped with IEEE 802.11p and LTE Uu could communicate via the cellular network. The challenge of the scenario case 3 (all new vehicles equipped with LTE PC5) would dictate ROs to add PC5-based RSU to existing RSUs potential. This means that vehicles without PC5 enabled would have to use V2I via smartphone. The case scenario 4 that predicts the use of Equitable 5.9 GHz would allow automotive OEMs to use IEEE 802.11 p for V2V/V2I and Cellular (LTE-Uu) for V2N. In conclusion, the base case (case scenario 1) and equitable 5.9 GHz RSU (case scenario 4) [19] deployment are thus suggested to be the most profitable way to deploy V2X services based on the net benefit perspective.  
The number of vehicles equipped with embedded C-V2X communication technology is expected to increase as shown in Figure 2. Even though after a while we would expect C-V2X to be equipped in a greater number of vehicles, vehicles which do not have embedded C-V2X would use LTE PC5-based smartphones for accessing V2I and V2P services. In this context, the base case (scenario 1) seems to be the one to be adopted by many automotive makers. A key challenge in this scenario is predicted when different automotive OEMs would deploy different V2V communication solutions. Consequently; the inefficient use of the equitable 5.9 GHz spectrum could occur due to no direct-communication interoperability of the two technologies (C-V2X and IEEE 802.11p).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Scenario\#**} & \multirow{2}{*}{**Description**} & **Vehicular** & **Remarks** \\ \cline{3-4}  & & **Communication** & **V2V** \\ \hline \multirow{3}{*}{Base case} & Adoption of C-V2X and IEEE & \multirow{3}{*}{V2V using IEEE 802.11p or} & \multirow{3}{*}{V2V is possible via cellular LTE} \\  & 802.11p in the absence of any & & LTE-V2X PC5 & \\ \cline{3-4}  & government measures & & \\ \cline{3-4}  & & & \\ \cline{3-4}  & In 2020, all new vehicles to support & & \\ \cline{3-4}  & ITS services via IEEE 2020 & & 802.11p for V2V and V2I & \\ \cline{3-4} Scenario 3 & In 2023, all new vehicles equipped & & \\ \cline{3-4}  & with LTE PC5 & & \\ \cline{3-4} Scenario 4 & Equitable 5.9 GHz use & & Division spectrum for V2V & \\ \cline{3-4}  & based PC5 and IEEE 802.11p & & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Use Case scenarios to study the penetration of V2X services. The study was carried out by Analysysys Mason [17].