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Link intermittent down caused by the border frequency which still within bandwidth got interference

Publication Date:  2012-07-25 Views:  59 Downloads:  0
Issue Description
  1. In H network, Hub link 110078 dir 110222 have dependency 60 sites.
  2. Link intermittent down when raining on site, RSL Level drop from -35dbm to -60dbm.
  3. First Line maintenance subcont unplug/plug the cable, reset the NEs.
  4. First Line maintenance subcont feedback bad weather condition on site.
  5. Frequency TX set to 7505 MHz at 110222 sides and bandwidth is 28 MHz.




Alarm Information
  1. MW_RDI Alarm occurs at 110222 side.
  2. MW_LOF Alarm occurs at 110078 side.
  3. BER was high.




Handling Process
  1. Interference test done by first line subcont with -90dbm RSL when mute far end at the 110078
  2. Suspect the installation not good, but confirmed by Fist line engineers, installation is good. ODU and IF board have been replaced with new one.
  3. Check with TNP team the Link budget using vertical but actually on site is horizontal, since at vertical having interference.
  4. Horizontal having more fade margin but confirm by TNP team that horizontal also OK after check the external environment by first line subcont.
  5. Check alarm again, suspect the interference at 110078 by the frequency not allowed by DGPT (Local government), but it is within the bandwidth.
  6. Analyze the bandwidth is 28M, frequency is 7505, need scan frequency from 7491 to 7519.
  7. Mute far end and check interference again at 110078, found interference at 7498 and 7501.5 frequency.
  8. Change the frequency to 7519 MHz according to DGPT (Local government.) regulation; monitor the performance and problem clear. All the frequency within bandwidth is have better condition for interference.




Root Cause
From the frequency scan result, Interference at 110078 side, in 7505, Interference clear, but consider the bandwidth 28MHz, it got interference at 7498 and 7501.5.

RTN XMC ODU only detect RSL in a stricture  bandwidth(Around 7Mhz or less than) then caucluate the RSL to 28MHz condition. For interference checking, should scan it from low frequency to high frequency, each 3.5Mhz, scan one time to get the real interference RSL level.

In this case,fequency scan result as bellow:

 Frequency RSL when Far End Mute
7498000 -627
7501500 -664
7505000 -900
7508500 -900
7512000 -900
7515500 -898
7519000 -882
7522500 -862
7526000 -864
7529500 -873
7533000 -896



Suggestions
  1. Interference check need to consider the bandwidth, it is possible the other operator not following DGPT (Local government) regulation.
  2. Revise the ATP document and share to first line maintenance team.




END