## 3 Economic Motivations, Applications and Requirements for VSNs  
Why are VSNs so hot? V2V communication in conjunction with automated vehicle technologies could provide a higher level of predictability than sensors, radar and cameras alone. V2V allows vehicles to share their intention (e.g., sudden lane changes) and exchange sensor data. The sharing of these types of information will help vehicles better anticipate and react to the movements of other nearby vehicles [2]. The importance of connected vehicles is also demonstrated by the fact that, for the first time, the European Commission (EU) adopted in November 2016 a European strategy on cooperative-intelligent transportation systems (C-ITS), to deploy vehicles that can \"talk\" to each other and to the transport infrastructure on EU roads as of 2019 [18], and, in December 2016, the National Highway Traffic Safety Administration (NHTSA), announced the proposal of an introduction of rules to mandate V2V communication on light vehicles from 2019 (as it will be better detailed in Section 5). Studies have estimated the market potential of cooperative, connected and automated driving to be worth dozens of billions of euro annually and the creation of jobs could run into the hundreds of thousands [18]. Connectivity, in fact, will provide important applications, which translates into new business model opportunities for municipalities, companies, and insurance, as well as road and connectivity infrastructure owners. A first insight into the deployment costs for V2X and revenue analysis for financially and socially beneficial commercialization are provided in [19], which represents the first outcome of the 5G-PPP Automotive working group. In [19], the authors provide an estimation of investment cost and profit for a 10-year horizon considering a 100 km highway segment with a traffic density of 100,000 vehicles/100 km per day, a 10% yearly penetration rate, a service fee of 1 Euro per vehicle with an income of 50% of the fee and a deployment cost made by the sum of raw capital expenditure (CAPEX) and operating expenditure (OPEX) considerations; they showed that it would be necessary five years after the initial investment to see some profit, but a profit of almost 70 MEuro can be expected in 10 years. Following similar considerations, in Figure 1, we plotted the achieved profit for different scenarios varying the traffic density and the service fee in 100 km highway and 100% penetration rate. We assume, as in [19], an income of 50% of the fee. As a raw estimation of deployment costs, we assume a CAPEX equal to 20 MEuro every 100 km and OPEX of 2.1 MEuro per year. It can be observed that the profit is negative only for the first year of the less dense scenarios with 50,000 or 100,000 vehicles with 1 Euro service fee. In five years, for example, and a density of 150,000 vehicles per day, the profit is over 100 MEuro. Of course, these are only qualitative estimations, but it is not difficult to think that, with a good business case, they may be helped by some mandatory rules, and the investment would provide high incomes. In Table 1, some example requirements of the main typical applications are reported. Table 1 refers to V2V applications, enabled by both the periodic exchange of beacon messages and event driven messages. We did not report in this paper applications based on vehicle-to-infrastructure (V2I); for requirements related not only to V2V applications, the reader may refer, for example, to [20]. From Table 1, it could be observed that the most stringent requirements are on beacon frequency (typically 10 Hz) and latency (typically less than 100 ms). In most of the applications, the throughput per link is not very stringent, although issues arise when the number of vehicles becomes high. It must also be underlined that all the application requirements reported require a reliability higher than 90%; in particular, for cooperative maneuvers, such as merging traffic turn assistance or lane changing, the reliability should be \(\geq\)99%.