Introduction:
Most of the mobile communication cannot be modeled by using freespace 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
Where:
L_{50}=50th percentile value of propagation path loss,
L_{F}=free space propagation loss,
A_{mu}=median attenuation relative to free space,
G(h_{te})= base station antenna height gain factor,
G(h_{re})= mobile antenna height gain factor,
G_{AREA}=gain due to the type of environment
 Okumura derived empirical formulas for G(h_{t}) and G(h_{r}) a
Hata Model:
 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, 1501500 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