## 1 Introduction
Other concepts used are Vehicle-to-Device (V2D), Vehicle-to-Grid (V2G), and vehicle to roadside units (RSU). RSUs are a particular type of V2I located on both sides of the avenue providing information and connectivity to nearby vehicles. Its applications include data disseminators, traffic records, security handlers, and service proxies. Although the inclusion of large amounts of sensors involves the creation of smarter vehicles, the fields of action of these sensors have their limitations. The adoption of cooperative systems between vehicles on the route would allow the sharing of unprocessed or semi-processed sensor data betweenvehicles, allowing the system to obtain more accurate information and make smarter decisions [8]. This real-time exchange of sensor data requires high communication performance, and with the increase in vehicle density on the road many simultaneous connections will also be required [9]. Future autonomous vehicles will also generate large amounts of data in areas such as high-speed internet, video streaming, online video games, and real-time map information. The massive traffic of data produced by these sensors will require transfer rates in magnitudes of gigabits per second to communicate with other vehicles or road infrastructure. This capacity will allow bringing cloud computing to the era of autonomous driving [10]. Consequently, the demand for wireless techniques that support this high bandwidth has increased considerably in recent years. Wireless connectivity with high transfer rates is predicted to be the next frontier in the vehicular revolution. Different technologies have been considered for the use of vehicular communication, some of these include Bluetooth, satellite radio, and communication through visible light. Despite these different technologies, the strongest candidates for the future of vehicular communication are the Dedicate Short Range Communication (DSRC) supported by the IEEE 802.11p standard and the use of the cellular mobile network (C-V2X) [11]. Although DSRC can ensure low-latency communication, its maximum transfer speed hardly exceeds 6 Mb/s in real applications. For C-V2X, higher transfer levels can be achieved, in practice usually values of 100 Mb/s, but communication latencies cannot get below 100 ms [12]. In recent years, significant academic activity, motivated by these requirements, has proposed the adoption of mmWave frequencies (i.e., 10-300 GHz) to support high transfer rates and low latencies [13]. Although the use of mmWave bands promises a significant increase in data rates with less latency, its use comes with high constraints for implementation. Free-space losses are very high at these frequencies, as a result, communication ranges will decrease considerably. The poor diffraction associated with these frequency ranges produces a more aggravated shadowing effect, this associated with the poor signal penetration, leads to deep losses due to objects in the communication path [14]. Wireless links at these high frequencies suffer from many deteriorating factors which pose challenges to the V2X communication system. In addition to these limitations, the high medium mobility and the relatively low height of the transceivers also increases Doppler effect phenomenon and occurrences of non-line-of-sight (NLOS) links. Due to its direct relationship with the relative speed of the transceivers, the Doppler effect is one of the most critical concerns in the use of mmWave in vehicular communications. The V2X propagation channel exhibits rapid temporal variability, and due to the dynamics of its physical environment, the statistics of the channel exhibit a non-stationary behavior, which makes the design of V2X systems in the mmWave frequency bands a challenging task. Further studies in these frequency bands are needed to understand the unique characteristics of vehicle communications, including gas attenuation, rain absorption, increased scatterers and reflections due to poor diffraction, and high penetration losses related to these frequency bands [9].