## 1 Introduction  
Radio 5G technology promises dramatic network speed improvements and super-fast connection times, defining new physical layer technologies based on beamforming, massive MIMO, and mmWave transmissions [1]. The use of millimeter-wave (mmWave) frequency for 5G communication systems is usually presented by the research community, but mmWave does have its challenges [2, 3, 4, 5]. The 5G technology specifies new frequency bands below 6 GHz and extends into millimeter-wave (mmWave) frequencies where more contiguous bandwidth is available for sending a lot of data. While users will appreciate the increased bandwidth, it introduces challenges, e.g., link quality requirements at mmWave frequencies. Often, these impairments are not an issue at sub-6 GHz, but become more problematic at mmWave frequencies [6, 7, 8]. Common signal impairments impact baseband and RF designs with wider channel bandwidths expected at mmWave frequencies [9, 10, 11]. These impairments become more problematic at higher frequencies or with wider bandwidths. According to IMT 2020 specifications, below 1 GHz, there are multiple bands of interest in 600, 700, and 800 MHz to support the internet of things and other mobile services. On the other hand, bands between 1 and 6 GHz aim to increase coverage and capacity. Above 6 GHz will primarily support the need for ultra-high broadband use cases [12, 13, 14]. In wireless mobile communication, two fundamental parameters determine its operation: Doppler spread--or time-varying nature of the radio channel--which causesfrequency dispersion, and multipath, which causes time dispersion and, therefore, its relationship to coherence time [15]. Doppler spread is more convenient to express in terms of power spectral density (PSD) in the Doppler spectrum (DS), resulting in the Doppler power spectrum (DPS), which characterizes this spectrum broadening caused by the time-varying nature of the wireless channel. In particular, 5G wireless mobile communications require reducing the DS due to user movement and increasing the coherence time (CT) simultaneously to achieve a better system performance when a 5G high-mobility user environment is required. In the technical literature, different models describe the Doppler power spectrum (DPS), the most consulted and cited are the [PERSON] model [16], the [PERSON] model [17], the Gans Model [18], and the IEEE P802.11 model [19]; they all define the DPS, depending on the carrier frequency and the speed of the mobile user. To assess the influence of high gain antenna arrays over DPS models, in [20], the authors describe radio propagation's statistical properties between a mobile terminal and a base station as a function of time, space, and frequency. In particular, a mathematical model that relates the DPS to the antenna gain when the main beam is focused along the perpendicular plane of the mobile terminal was conducted. Theoretical results in [20] conclude that, for all mobile station movement directions, the DPS is reduced when the width of the radiation beam from the base station to the mobile user is narrower or more directive. Nevertheless, the numerical analysis and results focus on highly narrow beamwidth values rarely found in small cells of wireless communications. On the other hand, a set of experimental measurements regarding the CT, in rural and road environments at a carrier frequency of 5.9 GHz, were presented in [21], demonstrating that the CT decreases, as a reverse relationship, according to the distance between the transmitter and receiver increases. Moreover, they determined that the Doppler power spread increases with the mobile equipment speed linearly and proportionally. Additionally, in [22], the coherence time (CT) was evaluated for the main antenna beamwidth under a wireless channel at 60 GHz in a millimeter frequency band. In [22], the numerical analysis and results are focused on determining the effects of the main antenna beamwidth over the CT, considering different pointing angles between the scatter ring and the mobile terminal.