## 5 Communication in Vehicular Networks
### Communication Types  
The heterogeneous nature of vehicular networks requires the implementation of various approaches to communication among vehicles and infrastructure. In this section, we present three approaches used in vehicular networks. Each approach is presented with its specifics, advantages, and disadvantages with appropriate use in specific scenarios; hence, vehicular networks frequently need to combine them with the goal of securing the most operational communication. They include the following:  
* **Direct communication:** The usage of direct communication is possible in cases when vehicles are intended to communicate with base stations. In this scenario, vehicles are not able to communicate directly with each other due to the centralization of a network [66]. This type uses base stations as central nodes, thereby simplifying network architectures. A significant disadvantage is the possible failure of a central node,  
Figure 3: Communication models within IoV network [63].  
which would result in a failure of the whole network. Furthermore, due to limiting the communication only to a central node, the network may be prone to performance issues such as bottlenecks and is not suitable for dynamic environments [67].
* **Satellite and cellular networks:** Communication via satellite and cellular networks plays a vital role in interconnecting multiple vehicles. While satellite networks are suitable for communication in geographically distant nodes and find their use especially in flying vehicle networks, their use is also viable for ground vehicles in areas with sparse infrastructure and outside of cities, where there may not be other means of communication either directly to other vehicles or to an underlying infrastructure in the case that a vehicle is located outside of the coverage of cellular or other wireless networks [68]. On the other hand, cellular network coverage can provide fast and seamless communication in areas with sufficient coverage and is widely used in both ground and aerial vehicles [69]. Compared to satellite networks, cellular networks offer greater data transfer speed, lower latency--which is especially true in new generation networks such as 5G or beyond-5G networks--and a lower cost of operation [70].
* **Ad hoc networks:** In order to mitigate the disadvantages of the previous methods of communication, vehicular networks implement ad hoc networks. This approach was the primordial method of communication in earlier vehicular networks. Building on the MANET, nodes in the network with this type of communication enable nodes to communicate directly with each other without a need for centralization of the network's components [71]. The usage of such a method is convenient, especially with more vehicles, with each viewed as an end system in proximity, thereby allowing them to remain connected even in the case that a vehicle reaches a point without a coverage of centralized components [72]. This method finds applications in both ground and aerial vehicle networks. Even though this approach to communication has several benefits in comparison to the previously discussed methods, its usage may be hindered by the rapidly changing dynamic topology of such a network. To alleviate those drawbacks, some works are focusing on designing routing protocols for those networks with the goal of fast and reliable delivery of data while lowering the cost of operation and energy consumption [51].