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Interference in the frequency bandwidth range causes change of the receiver sensitivity of the radio and loses of microwave link when a propagation event happens in RTN910-V1R1C02

Publication Date:  2012-07-25 Views:  68 Downloads:  0
Issue Description
There was a radio link which went down every morning over a specific period of the year. When the data were checking, it was discovered that this happened when the reception level was -55 dBm. The receiver sensitivity for the configuration of this radio was -70,5 dBm (7GHz, 128QAM, 28MHz), this means that the link should not have behaved in this way.

Alarm Information
MW_LOF, MW_LIM.

Handling Process
Taking into account the alarms, we could detect that there was a problem with the Link ID received in both stations and this is clearly a sign of some interference problem. Therefore, we need to detect where the interference was, that’s why we make a receiver power exercise, changing the values of the transmission frequency over the range of the bandwidth configured in the radio and making a table with the receiver power of each frequency.
Thanks to this procedure we were able to detect the problem. Afterwards, we chose a new frequency free of interferences and the problem was solved.  

Root Cause
The receiver sensitivity of the radio was modified because there was interference. Nonetheless, the interference was not in the central frequency, it was in a frequency contain in the operation bandwidth of the radio. This interference was not critical when the propagation medium did not have abnormalities, but when there were some events like heavy raining or other propagation phenomena the interference began to be important and the services started to suffer LowBER, HighBER or/and interruption because the receiver sensitivity changed from -70,5dBm to -55dBm.

Suggestions
Following you will find the procedure to detect the interference making a power receiver exercise:
  1. Mute the transmission of the ODUs at station B
  2. Taking into account the ITU recommendation, change the transmission frequency at station A, over the range of the bandwidth configured in the radio using steps of 3.5 MHz.
  3. Collect all the information in a table
  4. Unmute the transmission of the ODUs at station B
  5. Mute the transmission of the ODUs at station A
  6. Taking into account the ITU recommendation, change the transmission frequency at station B, over the range of the bandwidth configured in the radio using steps of 3.5 MHz.
  7. Unmute the transmission of the ODUs at station A
  8. Choose a new frequency free of problems
  9. Set the new frequencies and repeat steps “a” to “g”. If everything is all right, keep this configuration.

END