Prediction models

This article outlines the various propagation models currently used by the wireless industry for signal transmission at both 900 MHz and 1800 MHz. We start with the foundation of free-space transmission, followed by Picquenard’s multiple knife edge diffraction model. This leads us to the COST 231 Hata model, COST 231 Walfisch Ikegami and Sakagami and Microcell models.

Free Space

The free space path loss model is usually the reference point from which all propagation models are employed and is used for determining free-space path loss. It is based on a $1/R^2$ or 20-dB/decade path loss. The following equation shows the free-space or Friis equation:$frac\{P\_R\}\{P\_T\}=G\_TG\_Rleft(frac\{lambda\}\{4pi\; d\}\; ight)^2$ Equation 1.1

;where:$P\_R$ = power available at the receiving antenna
:$P\_T$ = power supplied from the transmitting antenna
:$G\_R$ = receiving antenna gain
:$G\_T$ = transmitting antenna gain
:$d$ = distance between two antennas in free space.
:$lambda$ = wavelength

Since loss is generally expressed in dB, Equation 1.1 can be written as:

$L\_f=\; 32.4\; +\; 20log(d)\; +\; 20log(f\_c),$ Equation 1.2

;where:$L\_f$ = free space path loss, in dB
:$d$ = distance, in km
:$f\_c$ = carrier frequency, in MHz

For 900 MHz and 1800 MHz equation 1.2 can be reduced to the form: $L\_f\; =\; A\; +\; Blog(d)$, where A is the path loss at 1km and B is the slope:

$L\_\{f\_\{900\; =\; 91.5+20log(d),$

$L\_\{f\_\{1800\; =\; 97.5+20log(d),$