## 3 Path Loss Models
\begin{table}
\begin{tabular}{p{56.9 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Author \& Ref. No.** & **Frequency** & **Environment** & **Observations** & **Future Scope** \\ \hline \multirow{6}{*}{[PERSON] et al. [24]} & \multirow{6}{*}{0.8 GHz to 70 GHz} & Urban and & The authors estimated the path loss at mmWave frequencies using a feed-forward deep neural network model. & Random search approach was considered for tuning the hyper-parameters. \\  & & & environments & The proposed model enhanced the mean square error and prediction accuracy. & Path loss for different transmitter and receiver distances needs to be calculated for mmWave frequency bands. \\ \hline \multirow{6}{*}{[PERSON], [PERSON] et al. [25]} & \multirow{6}{*}{mmWave Bands} & UMi, UMa, and RMi environments & MIMO uniform antenna arrays are used to estimate the angle of arrival, angle of departure, and power delay profiles at mmWave frequency bands. & Path loss for different transmitter and receiver distances needs to be calculated for mmWave frequency bands. \\ \hline \multirow{6}{*}{[PERSON], [PERSON] et al. [26]} & \multirow{6}{*}{28 GHz} & UMi, UMa, and RMa environments & Directional and unidirectional antennas are considered in the urban microcell region, and the angle of arrival, angle of departure, and power delay profiles are estimated. & The authors wanted to extend it for large-scale path-loss models. \\ \hline \multirow{6}{*}{[PERSON], [PERSON] et al. [27]} & \multirow{6}{*}{26 GHz, 28 GHz, 32 GHz \& Indoor Stairwell Environment} & Path loss, path loss exponent, and standard deviations were estimated for the considered stairwell environments in the indoor region. & Path loss estimation for multi-stair buildings is in the future’s scope. \\ \hline \multirow{6}{*}{[PERSON], [PERSON] et al. [29]} & \multirow{6}{*}{28 GHz \& 38 GHz, 38 GHz environment} & The authors estimated path loss in LOS and NLOS scenarios by considering steerable transmitting and receiving antennas in the outdoor environment. & Need to implement it for the mmWave and THz frequency bands. \\ \hline \multirow{6}{*}{[PERSON], [PERSON] et al. [31]} & \multirow{6}{*}{400 MHz to 1800 MHz to 1800 MHz} & \multirow{6}{*}{suburban environment} & Existing Hata model was considered to optimize the path loss. System performance is estimated using the relative error. & Path loss estimation and comparison using different path-loss models is needed. \\ \hline \multirow{6}{*}{[PERSON], [PERSON] et al. [32]} & \multirow{6}{*}{150 MHz to 1500 MHz} & Urban & Path loss was estimated and compared using the free space, Hata and Eigh path-loss models. The authors observed that the Hata model is the best path-loss model out of three models. & Need to implement it for the mmWave and THz frequency bands. \\ \cline{1-1} \cline{2-4}  & & Urban & In this paper, we estimated and compared path loss using the existing standard path-loss models in the mmWave frequency region in the future. \\ \cline{1-1} \cline{2-4}  & & Urban & Compared path loss using the existing standard path-loss models in the mmWave frequency region in the future. \\ \cline{1-1} \cline{2-4}  & & Urban & Compared path loss using the existing standard path-loss models in the mmWave frequency region in the future. \\ \cline{1-1} \cline{2-4}  & & Urban & Compared path loss using the existing standard path-loss models in the mmWave frequency region in the future. \\ \cline{1-1} \cline{2-4}  & & Urban & Compared path loss using the existing standard path-loss models in the mmWave frequency region in the future. \\ \cline{1-1} \cline{2-4}  & & Rural Macrocell, and Rural Macrocell & Possible environments. & \\ \hline \end{tabular}
\end{table} 
Table 1: _Cont._based mobile radio access networks or 5G integrated communication (mmMAGIC) [19]. The PL in these models depends on the range between transmitter and receiver (T-R), carrier frequency, and environmental conditions. UMi, UMa, and RMa environments under LOS and NLOS scenarios are considered to estimate the PL and RP.