Prediction models

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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.

[edit] 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 / R2 or 20-dB/decade path loss. The following equation shows the free-space or Friis equation: \frac{P_R}{P_T}=G_TG_R\left(\frac{\lambda}{4\pi d}\right)^2 Equation 1.1

where
PR = power available at the receiving antenna
PT = power supplied from the transmitting antenna
GR = receiving antenna gain
GT = transmitting antenna gain
d = distance between two antennas in free space.
λ = wavelength

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

L_f= 32.4 + 20\log(d) + 20\log(f_c)\,      Equation 1.2

where
Lf = free space path loss, in dB
d = distance, in km
fc = carrier frequency, in MHz

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

L_{f_{900}} = 91.5+20\log(d)\,

L_{f_{1800}} = 97.5+20\log(d)\,