Table 6.

Comparison of various propagation models in millimeter wave for the indoor office environments.

Ref	Frequency (GHz)	Environment	Scenario	Models	Result	Observation
[47]	6.5, 10.5, 15, 19, 28 and 38	Indoor	NLOS and LOS	Frequency attenuation model CIX, ABG and ABGX	The results indicate that the value of the path loss exponents for the models adopted is lesser compared to the value when the model is in a free space, which is applicable for all the frequencies. The values were within 0.1–1.4.	This new proposed model shows its simplicity, lesser path loss exponent and has a god RMS delay spread and dispersion factor value.
[48]	4.5, 28 and 38	Indoor office	NLOS and LOS	New improved model	It shows that there is a better result of path loss when modelled with one parameter.	The result should be modelled with more than one parameter to actually know the stability at multiple frequencies.
[55]	Varying frequency	Indoor and outdoor	NLOS and LOS	A scheme that adopts mode assignment by reuse	It uses D2D communication with a good values of SINR.	The major advantage of this model is that it helps in a situation when there is problem of path loss attenuation in both indoor and outdoor environment.
[57]	Varying frequency	Indoor	LOS and NLOS	Indoor localization approach	There is a major improvement in the environment at different distances when compared to the existing schemes.	It only considers the distance and path loss. Frequency is another major factor that needs to be considered.
[64]	Varying frequencies	Indoor short office range	NLOS and LOS	Empirical path loss models	It shows appreciable varying values of path loss at different frequencies which also shows less complexity.	There is a need to test this novel prediction path loss, model in a commercial environment where more obstructions will take place.