Simplified Path-Loss Model
Signal propagation is a very complex phenomenon that we cannot obtain a single model to characterize the path loss accurately in different environments.
Calculation of the Path loss in Simplified Path-Loss Model
For general trade-off analysis of various system designs it is better to use a simple model that captures the essence of signal propagation
Thus, the simplified model for path loss as a function of distance is commonly used for system design
The dB attenuation is thus
K is a unitless constant that depends on the antenna characteristics and the average channel attenuation, d0 is a reference distance for the antenna far field, and γ is the pathloss exponent.
When the simplified model is used to approximate empirical measurements, the value of K < 1 is sometimes set to the free-space path gain at distance d0 assuming omnidirectional antennas
and this assumption is supported by empirical data for freespace path loss at a transmission distance of 100 m.
The Value of K can be determined by measurement at d0 oroptimized (alone or together with γ) to minimize the mean-square error (MSE) between the model and the empirical measurements.
The value of γ depends on the propagation environment: for propagation that approximately follows a free-space or two-ray model, γ is set to 2 or 4 (respectively).
The value of γ for more complex environments can be obtained via a minimum mean-square error (MMSE) fit to empirical measurements as you can see in table given below