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: 
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:
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:
