The study of mm-wave propagation, i.e. both attenuation and directional characteristics, are important for 5G and beyond wireless communication system design and network deployment   . Besides, site-specific propagation studies are useful to ascertain optimum coverage of network base stations . In addition, scenario-specific study of mm-wave propagation loss and directional spread is desired to provide reliable services in, for example, high speed trains . Also, to overcome the high attenuation at mm-wave frequencies, directional antennas and beamforming are used and thus we require to know the directional spread characteristics of the wave at these high frequencies  .
In 5G and beyond wireless communication network deployment and optimization, there is a problem of accurately estimating the field distribution and directional spread of mm-wave propagation . Millimeter wave signals are highly attenuated by building materials and vegetation and thus the propagation range is relatively small. That means millimeter wave signals experience high path loss when propagated through long distance and complex environments. Also, the reflection characteristics of building materials depend on polarization, electrical properties of materials, antenna beam width, building structures and location of transmitter and receiver . Thus, the attenuation of mm-waves in outdoor scenarios due to buildings and vegetation are more severe than for classical microwave frequencies . Radio waves propagate in different paths with different delays. Hence, these multipath signals do not align with the line-of-sight signal and the combined signal will be smeared in time causing delay spread. Delay spread is the second moment of multipath power delay profile and causes inter symbol interference (ISI) . Consequently, the spread in directivity of mm-wave signals with increased coverage requires us to study the directional spread characteristics to determine the spacing between base stations for collaborative operation, i.e. the spatio-temporal distribution of the waves is a key planning factor. This will help us in spatial scanning of mobiles by massive and smart base-station antennae . Importantly, to adequately assess the performance of 5G and beyond wireless systems and networks, there is a need to develop mm-wave path loss and directional spread models .
Ray tracing method is based on geometrical optics, geometric theory of diffraction, and uniform theory of diffraction used to predict the propagation properties of radio wave  . An-Yao Hsiao in presents an urban outdoor ray tracing simulations using global ray tube approach rather than using individual rays and hence the method has better computational efficiency. In addition, in this work, field measurements were made and these data were used to calibrate the ray tracing simulation. Here, although similar results were obtained in both approaches, fast fading behaviors are different. However, the work did not address the directional spread characteristics of mm-wave signals, which affects the performance of 5G and beyond networks. The work in empirically investigated the directional multipath propagation characteristics of mm-waves for a typical urban scenario. Specially, it determined delay and angular spread. Further, microcellular radio channel characterization is measured at 60 GHz as presented in using directional steering antennas at the mobile end. In this work, path loss and delay spread strongly depend on the antenna pattern. Nevertheless, the approach is expensive and time consuming especially it becomes prohibitively expensive for closely spaced 5G and beyond base stations. Finally, the work in presented a combination of empirical measurement and ray tracing methods to predict path loss at various mm-wave frequencies. But, it did not deal with the directional characteristics of mm-waves as function of distance between transmitters and receivers. In , studies of outdoor propagation with different scenarios at 60 GHz frequency bands is carried out. This work considered scattering and diffraction as the main propagation phenomenon causing sever multipath in an urban scenario. The work deduced that, in urban environments, path loss and delay spread can be reduced substantially and are a function of antenna directivity and transmitter-receiver separation. The propagation characteristics of outdoor wireless channels at 28, 39, 60 and 73 GHz are studied for Line of Sight (LOS) and Non Line of Sight (NLOS) in . The authors in this work concluded that LOS has a high receiving capacity and lower path losses than NLOS. Also, they found out that high frequencies are affected more than low frequencies and that meant increase in the path loss and decrease in the received power.
Currently, ray tracing is preferred for propagation modeling more than other methods such as the empirical models. It can be applied to many of the propagation scenarios in wireless communications and play an important role in the future propagation modeling tools. This is because it is useful for tackling complicated propagation environments at high frequencies . In our paper, the economic approach of predicating attenuation (path loss) and directional spread are investigated using an advanced ray tracing technique. The technique can realistically and economically be done for all base-stations of a typically 5G and beyond network. The rest of the paper is organized as follows. Methodology is described in Sect. 2. The simulation result on path loss, delay spread, and power delay profile parameters are analyzed and discussed in Sect. 3. Finally, Sect. 4 summarizes our findings.