Motorola PTP 400 Series - Manual (Page 48)

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6.1.3 Path Loss Considerations
The path loss is the amount of attenuation the radio signal undergoes between the two ends
of the link. 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).
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)
Equation 1 - Path Loss
6.1.4 Aggregate Ethernet throughput rate versus maximum link loss
The equipment capability is given in Table 8 and Table 9. It gives the Ethernet throughput
rate versus link loss for the PTP 400 Series Bridge in both modes. Adaptive modulation will
ensure that the highest throughput that can be achieved instantaneously will be obtained
taking account of propagation and interference. The calculation of Equation 1 needs to be
performed to judge whether a particular link can be installed. 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.
The full calculation is relatively complicated and thus Motorola has supplied a PTP Link
Estimator that calculates the radio propagation and reliability of NLOS links using the PTP
400 Series Bridge equipment.