They can be widely used in urban, rural, and even indoor environments, but their accuracy is limited to the range of the data measured, so they may not be precise when applied to other environments, and their use requires careful consideration. One of the best-known of this type is the Okumura-Hata model, which in its original form and constants is suitable for estimating path loss between 150 MHz and 1500 MHz. It was later extended to the 1500 MHz and 2000 MHz frequency ranges as the COST 231-Hata model [8; 9]. Given that Mobile/Fixed Telecommunication Network (MFCN) systems are allocated in increasingly higher frequency bands, the need to retune these models has also opened up. This is possible, for example, by redefining the parameters of the Okumura-Hata and COST 231-Hata models using optimization algorithms in order to better fit the measurement results in the pioneer MFCN bands [10]. A similar model is the Stanford University Interim (SUI) model [11], which can be applied to higher frequencies than the COST 231-Hata model [12]. However, a research gap has been identified to tune this model more accurately for the 6 GHz frequency band in order to better fit the outdoor wave propagation properties of this frequency band than is given in its present form. The second large group of wave propagation models regards deterministic wave propagation models. These models are based on mathematical equations describing the propagation of electromagnetic waves as a physical phenomenon, which can be derived from [PERSON]'s equations. They provide accurate predictions with detailed and precise consideration of the terrain and environment, and are not frequency-specific. They have the disadvantage of being more computationally complex than empirical models, especially when considering larger areas and more advanced cases [13]. One such widely used method is the Parabolic Equation Modeling (PEM), which is based on the numerical evaluation of parabolic equations. It is mainly used for modeling long-range radio wave propagation and topography effects. The model is based on a special approximation of [PERSON]'s equations [14]. Although in this paper we are dealing with PE, it is worth mentioning that there are many other deterministic models, among which the Ray Tracing method is widely used [15], as well as the Finite-Difference Time-Domain [16] (FDTD) and the Method of Moments [17] (MoM), noting that the last two are not typically used for long-range wave propagation problems due to the high computational capacity required. It is important to point out that there are also so-called hybrid-type, i.e,semi-empirical or semi-deterministic, wave propagation models, which combine the advantages and disadvantages of the two large groups, with specified compromises. In this paper, we consider the ITU-R P.452-17 wave propagation model [18], which can be used as a hybrid model for both the 3.6 GHz and 6 GHz frequency bands, as well as the 3 GPP 38.901 model [19]. The comparison, advantages and disadvantages of each group of wave propagation models are shown in Table 1.  
As mentioned earlier, in this paper, the analysis of wave propagation models is limited to outdoor wave propagation phenomena, mobile telecommunication networks, and two frequency bands, 3.4-3.8 GHz and 6 GHz. The 3.4-3.6 and 3.6-3.8 GHz frequency bands are globally allocated on a co-primary basis for mobile services, except for aeronautical mobile, according to the Radio Regulations (RR) [20]. According to the European Table of Frequency Allocations and Applications (ECA Table), both bands are allocated for mobile service, supporting their use for terrestrial mobile networks in Europe [21]. Based on European Commission Implementing Decisions [22; 23], the 3.4-3.8 GHz frequency band has been harmonized for terrestrial systems capable of providing electronic communications services in the European Union, and the harmonized frequency arrangements as well as the least restrictive technical conditions for MFCN have been also defined in ECC Decision (11)06 [24].