Most of the mobile communication cannot be modeled by using free-space path loss or ray tracing because these systems operate in complex propagation environment.These models are mainly based on empirical measurements over a given distance in a given frequency range and a particular geographical area or building
Empirical path loss models
- Empirical measurements of Pr/Pt as a function of distance include the effects of path loss, shadowing, and multipath.
- In order to remove multipath effects, empirical measurements for path loss typically average their received power measurements and the corresponding path loss at a given distance over several wavelengths
- This average path loss is called the local mean attenuation (LMA) at distance d, and generally decreases with d due to free space path loss and signal obstructions.
The Okumura Model:
- Okumura's model is one of the most widely used models for signal prediction in urban areas.
This model is applicable for
- frequencies in the range 150 MHz to 1920 MHz
- distances of 1 km to 100 km
- The model can be expressed as
L50=50th percentile value of propagation path loss,
LF=free space propagation loss,
Amu=median attenuation relative to free space,
G(hte)= base station antenna height gain factor,
G(hre)= mobile antenna height gain factor,
GAREA=gain due to the type of environment
- Okumura derived empirical formulas for G(ht) and G(hr) a
- The Hata model is an empirical formulation of the graphical path loss data provided by Okumura and is valid over roughly the same range of frequencies, 150-1500 MHz
- The standard formula for empirical path loss in urban areas under the Hata model is
- For a small to medium sized city, the mobile antenna correction factor is given by
- for larger cities at frequencies fc > 300 MHz by