## 1 Introduction
Moreover, higher frequencies are more easily absorbed by the atmosphere, hence being scattered and absorbed by weather events and buildings, which demand nearly a line-of-sight (LOS) communication [17; 18]. It has been predicted that the 5G mmWave would need a massive amount of small-cell deployment, hence the requirement for very small, directive, and high-gain antennas. Besides, free-space propagation is deemed to suffer extremely high attenuation losses due to the small signal wavelength [19]. The design of compact, high-gain, and steerable antennas for 5G devices is another potential challenge in realizing mmWave communication. The direction of the pointing vector of electromagnetic waves, especially for non-line-of-sight (NLOS) environment, is critical to attain maximum quality of service (QoS) performance [20; 21]. The 5G network performances are in line with this objective. First, it has a data rate, where 10 Gbps is supported in the cellular area and 1 Gbps at cell-edge, which refers to the location with the worst performance [22; 23]. Second, the spectral efficiency has to boost up in order to accomplish 10 bits per second per Hertz [24]. Besides, while achieving higher capacity, it must support more than a million devices after taking into account vehicle IoT, smart devices, wearable devices, and smartphones within a one-square kilometer area [25]. High mobility and very small latency, for example, to support vehicles, trains or aircrafts moving at 300 to 500 kilometers per hour, have to offer end-to-end service upon data request, which requires delivery within 5 milliseconds (ms), whereas from the access point to the device, it should be below 1 ms [26]. In order to accomplish this, the 3 rd Generation Partnership Project (3 GPP) and the International Telecommunication Union (ITU) is expected to set 5G standards; the 3 GPP Release-16 is not expected until 2020 [27; 28]. The core technologies under consideration for the 3 GPP Releases seem to work on a new waveform design, multi-RAT interworking, exceeding 6 GHz frequency band, massive MIMO antenna configuration, as well as advance D2D and flat network [24]. For the perfect channel condition, the receiver must receive the best signal-to-noise ratio (SNR) value. This is possible when one can receive a transmitted signal without attenuation, loss or noise. However, due to the unpredictable behavior of a wireless channel, the signaling overhead causes various serious issues when the propagation signal is continuously varying. In addition, when we are propagating the signal in a large number of antennas, the multipath propagation system delivers better spectral efficiency with a promising capacity gain [29]. In order to achieve optimal detection, generally, perfect Channel State Information (CSI) is assumed to be between the transmitter (Tx) and receiver (Rx). However, in practice, due to the mobility of the communication environment, the impulse response of the channel varies, thus inducing the need for channel estimation. In addition, permanent feedback signaling is required to notify the estimated CSI at the Tx, and many time slots are engaged during the feedback, thus reducing the bandwidth efficiency of the system. In real-world cellular environments where most users communicate to base stations (BSs) through channels with no LOS path, having access to precise geometric information regarding the relative locations of the BSs and users that yield high spectrum efficiency [30]. Therefore, the propagation behavior of the channel has a vital role in this situation, because the response of the propagation signal can be predicted [31]. Thus, in order to critically study the performance of the future 5G mmWave wireless network, analyzing the features of the propagation channel and its behavior is essential [32]. The aim of any reliable communication is to achieve a reliable (i.e., accurate) transmission link between the Tx and the Rx [33], including path loss, which is a major aspect upon assessing various types of network scenarios [34].