path loss
Path loss is the effect that traveling through space has on the signal.
A simple model of path loss is
r(t)=ℜ(λ√Ge−jd2πλ4πdu(t)ej2πfct)
where G is the product of the antenna field radiation pattern in the LOS direction (has to do with antenna aperture)
From this eq, the ratio of transmit to recieve power is
PrPt=(√Gλ4πd)2
Common model for large urban areas is the okumura model.
A simplified model is
Pr=PtK[d0d]γ
where K is a constant, d0 is the reference distance from farfield, and γ is the path loss exponent (comes from existing tables of empirical data).
This model is quite commonly used.