Vol. VI-B-32 Alcatel-Lucent
Probable Cause
The most common cause is path degradation through rain fade, diffraction, or
multipath. Other causes are equipment malfunction or interference.
Recommended Actions
1. Check for other alarms, particularly those that indicate a component failure,
or a complete path failure:
• Component failure or Rx path failure alarms must be checked before
investigating a BER Threshold alarm.
• If the only other alarms are Demodulator Not Locked, and its downstream
path failure and path warning alarms, a path failure is indicated, which
may be caused by a complete path fade or a remote Tx failure.
2. If BER Threshold Exceeded is the only active alarm, apart from other G.826
path warning alarms, check G.826 and RSL measurements at both ends using
the CT Performance screen:
• If low RSL and G.826 alarms are present at both ends of the link, a path
problem is indicated, which is most likely caused by a degraded path due
to rain, diffraction or mulipath fading. Prevailing weather conditions
should provide clues to support such conditions. If low RSLs remain
(permanent at both ends) a change in path parameters is indicated, such as
an antenna out of alignment, or an obstacle in the signal path. If there have
been abnormal weather conditions such as exceptionally strong winds,
suspect antenna alignment.
• If BER Threshold alarms are present at just the local end and RSL is
normal, a failure in the modulation process at the remote end, or
interference from another link should be suspected:
- Check remote-end LINK/RAC Tx alarms. An equipment problem is not
normally fleeting, meaning the Event Browser screen should show a
permanent alarm with a definite starting point.
- A newly installed interferring link should show a repetition of G.826
alarm occurences as it is installed and commissioned. Use the CT
History and Event Browser screens to track the onset of BER alarms.
3. If BER alarms coincide with low RSL and just one end of the link is affected,
a remote RAC or ODU equipment problem is indicated. Check remote
Detected Forward Power and Tx alarms.
Additional Information
A 10
-3
BER threshold alarm is preceded by 10
-6
BER threshold alarm.
Rain fade is the likely cause of fade for links 13 GHz and higher. Diffraction and
multipath/ducting for links 11 GHz and lower. If these alarms are persistent,
there could be a problem with the link design or original installation.
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