The general formula used to determine the power received at a certain distance from a transmitting antenna is called the Friis Free Space equation. This is given by the equation:
where
Pt = transmitted power
Gt = gain of transmit antenna
Gr = gain of receive antenna
d = distance (m)
Log Form of Friis Free Space Equation
The log form of Friis Free Space equation is given as
where
Pt = transmitted power
Gt = gain of transmit antenna
Gr = gain of receive antenna
d = distance (m)
Rref = reference distance (m)
Rref is defined to be 1 m. Excess loss has been added to account for extra losses due to the environment terrain, losses in the physical devices, and all other unaccounted losses.
Excess Loss
The amount of excess loss can be predicted using mathematical models and techniques to achieve a more accurate prediction of the received power. The models I used are discussed in the next section.
