## 1 Introduction
The International Telecommunication Union (ITU) and the World Radiocommunication Conference (WRC) have identified different mmWave frequency bands for terrestrial systems delivering high-throughput, low-latency 5G services [15]. These bands are: 24.25-27.5 GHz (24 GHz), 37-43.5 GHz, 45.5-47 GHz, 47.2-48.2 GHz, and 66-71 GHz. The V-band of 60 GHz is not in the above list given that it is reserved for the WiGig standards WiFi 802.11 ad and WiFi 802.11 ay [16; 17; 18; 19]. The 5G Phase 2 or Beyond 5G also contemplates V2X communications as use cases in mmWave frequency bands. This is due to the fact that cellular and WiGig current standards are not enough for the requirements of the specific types of V2X applications which demand extreme connectivity performance: ultra-low latency (less than 1 ms delay), high security, ultra-reliable connectivity for safety applications, and enhanced mobile broadband in order to provide augmented reality (data rate over 1 Gb/s) [20; 21]. Only mmWave bands can support ultra-high-speed mobile broadband demanded for 5G automotive use case [22]. The use of mmWave bands for vehicular communication is particularly attractive for future applications of ITS. The use of directional antennas and multiple-input multiple-output (MIMO)systems will require beam alignment, in a vehicular environment with high mobility, the appropriate design for beam tracking and prolonged link establishment is a highly complex task. The reduction in the communication radius will be subject to regular handovers, and due to the constant change of the communications channel as well as the sudden appearance and disappearance of scatterers, there will also be high restrictions in time to perform such handovers. Identity authentication and establishing a trusted connection with the cloud will be a difficult task in a V2X network [23]. The abstraction of the characteristic parameters in the electromagnetic transmission channel towards propagation models can shed light on the complex propagation mechanisms in mmWave bands and allow the evaluation of the designed communication systems [24]. Nevertheless, due to the propagation differences between micrometer waves and mmWave, the propagation models used in vehicular environments for under 6 GHz systems cannot be used in scenarios for mmWave frequency bands. Thus, achieving effective communication in mmWave links for vehicular environments requires a deep understanding of the vehicle communication channel. This calls for new models that account for the specific characteristics of communications in the millimeter frequency bands. To this end many propagation models has been developed in the literature, taking into account the availability or not of geometric information of the environment. In this sense, the main approaches can be classified as deterministic or stochastic geometric models and stochastic or empirical non-geometric models. Empirical models are based on approximations resulting from the collection of experimental measurements, they are simple, relatively effective, and accurate, for environments that resemble some of the characteristics in which the measurements were made. The input parameters for the empirical models are usually very general (e.g., urban area, rural area). One of the main disadvantages of these models is that they must be employed in environments similar to those used in their estimation, requiring strong modifications for their use in other environments, and in many cases, they are simply ineffective outside of these scenarios [25]. Some empirical studies regarding sub 6 GHz vehicular propagation channels can be found in the literature like [5; 26; 27]. Non-geometric stochastic models (NGSCM) are used to predict the values regarding the modeled system, taking into account the occurrence of random elements within the system. They are designed to simulate uncertainty in different scenarios. These models can be relatively versatile to describe propagation channels in different environments.