Talk:Prediction models

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Tried to improve the appearance of the later equations. Removed the original poster's warning, "NOT FINALIZED, I HAVE PROBLEMS FORMATTING THE EQUATIONS", but somebody with more knowledge than I should check the equations for errors or more conventional formatting. Kevinz 19:26, 5 March 2007 (UTC)

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: ${\frac {P_{R}}{P_{T}}}=G_{T}G_{R}\left({\frac {\lambda }{4\pi d}}\right)^{2}$ 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:

$L_{f}=32.4+20\log(d)+20\log(f_{c})\,$      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: $L_{f}=A+B\log(d)$, where A is the path loss at 1km and B is the slope:

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

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