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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).
L
Where
L
L
L
L
L
6.1.4
Definitions
The equipment capability is given in Table 9, Table 11 (IP Mode) and Table 10, Table 12
(TDM Mode). Each table gives Link Loss, Output Power and System Thresholds for PTP 500
Series Bridge in all modulation 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.
For minimum error rates on TDM links the maximum modulation mode should be limited to
64QAM and channel coding rate of R= 0.75, denoted as 64QAM 0.75.
+
+
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
Equation 1 - Path Loss
+
<
L
L
seasonal
capability
50
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