Path Loss Considerations; Calculating Path Loss; Adaptive Modulation - Motorola PTP 500 Series User Manual

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.
L
Where
L
L
L
L
L

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.
Equation 2 - Path Loss
+ +
L L
free _ space excess fade
Free Space Path Loss (dB)
free _ space
Excess Path Loss (dB)
excess
Fade Margin Required (dB)
fade
Seasonal Fading (dB)
seasonal
Equipment Capability (dB)
capability
+ <
L L
seasonal capability
37
4 Planning Considerations