Free Space

Free space path loss is usually the reference point for all the path loss models
employed. Each propagation model points out that it more accurately
predicts the attenuation experienced by the signal over that of free space.
The equation that is used for determining free space path loss is based on
a 20 dB/decade path loss. The free space equation is as follows:

Lf = 32.4 + 20 log (R) + 20 log (f)
where R =km, f=MHz and Lf=dB

The free space path loss equation has a constant value that is used for
the air interface loss, a distance and frequency adjustment. Using some
basic values, the different path loss values can be determined for comparison
with other models that will be discussed.