Alcatel-Lucent 9500 MXC User Manual page 759

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10 BER threshold exceeded
Probable Cause
Recommended Actions
3DB 23063 ADAA - Rev 004 July 2007
Check that all other link health indicators are normal before investigating an
interference problem. Then check for any new link installations in the same
geographical area, on the same frequency band, which coincide with the onset of
BER alarms. Confirming interference may require use of a spectrum analyzer.
Received data has exceeded a threshold of 1 error bit in a data stream of 10
(0.0001% error rate). This is a warning alarm.
The most common cause is path degradation through rain fade, diffraction, or
multipath. Other causes are equipment malfunction or interference.
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.
9500 MXC User Manual
6
bits
Vol. VI-B-33