Towards a Novel Air-Ground Intelligent Platform for Vehicular Networks: Technologies, Scenarios, and Challenges  
[PERSON]  
1 Department of Electrical, Electronic and Information Engineering \"[PERSON]\", University of Bologna, 40136 Bologna, Italy; [EMAIL_ADDRESS]  
1 Corresponded: [EMAIL_ADDRESS]  
2  
[PERSON]  
1  
Footnote 20: email: {daniof users [2, 3, 4, 5]. However, vehicle onboard computation capacity is falling short when new latency-critical and data-intensive applications are considered; hence, new challenges are arising in VNs. The Cloud computing facilities are able to reduce the computation burden of new services; therefore, Vehicular Users (VUs) can transmit the portion/complete task to the cloud servers having enormous computation and communication power. In general, the cloud facilities are located far from the users, in the core network, and introduce some drawbacks, e.g., huge transmission costs, backhaul link congestions, data security threats due to long-distance communications. Such issues can be addressed by integrating the Edge Computing (EC) facilities into VNs, bringing cloud computing resources in the proximity of end-users [6, 7]. In the case of VNs, EC facilities can be integrated through the deployment of several EC servers alongside the road network co-located with Roadside Units (RSUs). Such an approach is known as Vehicular Edge Computing (VEC) and has achieved lots of success by enabling new latency-critical services into VNs [8]. However, the limited capacity and coverage of EC servers/RSUs is the main bottleneck while exploiting VEC advantages. VEC-based VN can also be complemented by adding additional EC servers located on the terrestrial cellular base stations (i.e., 5G-gNB). Such ground-based multi EC platforms can compliment VUs by providing additional services and reducing the overall burden of the VEC servers. However, in recent times, Terrestrial Networks (TNs) are becoming more and more used, with many new users requesting services with specific demands. Limited coverage into rural and remote areas, unreliable service during natural disasters like tsunamis and earthquakes, new security challenges, poor link budget with additional interferences are some of the main challenges that need to be considered while utilizing TN-based EC platforms into VNs. In addition, VUs are not the only user group requesting services from the TN-based EC platforms. With the presence of different users, the dynamically changing resources of EC servers with vehicular mobility adds additional challenges while integrating the TN-based EC services into VNs. With this limitation, integrating TN-based EC platforms into VN alone can not be a sufficient solution for the new futuristic vehicular services and applications, which will have more stringent requirements in terms of latency and computation resources. Encouraged by the new technological developments and the additional interest shown by several tech giants (i.e., Facebook, Google, etc. ), the Non-Terrestrial Networks (NTN), including space and air networks are growing these days mainly for providing global connectivity [9]. Several new platforms such as new satellite constellations, unmanned aerial vehicles (UAVs) swarms, small fueled aircraft, balloons have been deployed at different heights from the ground users to achieve the global connectivity challenge [10]. Better connectivity, scalability, reliability are some of the advantages of NTN based communication platforms. With the addition of modern communication technologies, such as multi-beam antennas, the NTN platforms can also provide EC-based services with an onboard computing server [11, 12, 13]. Such NTN-based EC platforms can complement the VNs for solving several problems, including RSUs' limited capacity and coverage. However, the higher transmission delay, introduced by space networking platforms (i.e., satellite constellations), is a major challenge while considering NTN platforms for serving latency-critical VNs.