4 Planning Considerations
37
4.8 Path Loss Considerations
Path loss is the amount of attenuation the radio signal undergoes between the two ends of
the link.
4.8.1 Calculating Path Loss
The path loss is the sum of the attenuation of the path if there were no obstacles in the way
(Free Space Path Loss), the attenuation caused by obstacles (Excess Path Loss) and a
margin to allow for possible fading of the radio signal (Fade Margin). The calculation of
Equation 2 needs to be performed to judge whether a particular link can be installed.
Equation 2 - Path Loss
capability
seasonal
fade
excess
space
free
L
L
L
L
L
<
+
+
+
_
Where
space
free
L
_
Free Space Path Loss (dB)
excess
L
Excess Path Loss (dB)
fade
L
Fade Margin Required (dB)
seasonal
L
Seasonal Fading (dB)
capability
L
Equipment Capability (dB)
4.8.2 Adaptive Modulation
Adaptive Modulation ensures that the highest throughput that can be achieved
instantaneously will be obtained, taking account of propagation and interference. When the
link has been installed, web pages provide information about the link loss currently measured
by the equipment, both instantaneously and averaged. The averaged value will require
maximum seasonal fading to be added, and then the radio reliability of the link can be
computed.
4Gon www.4Gon.co.uk [email protected] Tel: +44 (0)1245 808195 Fax: +44 (0)1245 808299