Page 209 - GuideFWA

proponents’ view about this matter, and details why Fading margin for the useful signal should
be included in calculations:

“[…] fading margin allows to system operators to use a margin above the minimum
Operational RX Power in the planning to assure that most of the RXs (e.g. 99% of availability)
receive a useful signal at a level which have been indicated […] as “Mean RX Power” in order
to prevent the fade occurrences.

This is the actual way to design a system. Therefore we can assume that it is very likely that a RX
in a system, located at any place of the system coverage, is operating over a minimum received
useful signal equal to this “Mean RX Power” (i.e. including fading margin), because system
deployment has been designed to met this performance.

[…] if Fading Margin is removed from our calculation we can assure that only in an small
percentage (e.g. 1%) of time, the RXs can be affected by the anticipated interference level.

The interpretation of this affirmation is that, if we remove fading margin from calculation, it is
practically unlikely (e.g. a very few probability of 1%) that the anticipated interference will be
still harmful to a victim RX. While, if fading margin is not removed, there will be a probability of
50% (at the cell edge) that the anticipated interference is still harmful to a victim RX.

HOWEVER THIS INTERPRETATION IS ALSO VALID WHEN SYSTEM IS ALONE AND
THERE IS ONLY INTERNAL INTERFERENCE.

Then, which approach should be applied?

I think that we have to follow the same approach than the used when system is alone and
external interference does not exist.

If system is alone, when experiencing a say x dB fade of the desired signal, it is equally probable
than internal interferer signal is unfaded and would be x dB higher than the anticipated level.
Then system USES its mechanisms against interference (e.g. handover, dynamic channel
allocation, etc.) to avoid the undesired situation.

THIS IS THE NORMAL BEHAVIOUR OF A SYSTEM. When analysing the effect of External
Interference, the behaviour SHOULD BE the same. The effect of the external interference is
already taken into account by increasing the margin for interference (C/I), but removing the
fading margin we are ARTIFICIALLY increasing the constrains to the level of external
interference. Note that this constrain IS NOT applicable to the Internal Interference when system
in working alone.

There are several reasons why the fading margin is considered when system is working alone
(and it is not removed from any link power budget calculation) . These reasons are equally
applicable when an external interference appears. Some of these reasons are:

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