acceptable interference level microwave transmission

[akie_cool]

Dear all,


I have a question to ask, and i'm dealing with interference problem in 1 link SDH microwave transmission. I got RSL (let say) site A -41 dBm, but after interference test measurement, it still got RSL from somewhere else and measured RSL when the opponent's site is turned off with -70 dBm interference level.
Is it acceptable or not, what is the formula to know wheter the interference is good and acceptable or not.

Thanks in advance

[byja]

This certainly isn't acceptable. Given the facts that it's SDH link, I guess it's rather important. Also, it's probably using 128 QAM, and SNR required for such a link is at least 26 dB. Your SNR is 29 dB, so you have a margin of only3 dB. It also means that your threshold degradation is more than 20 dB. Normally, acceptable TD is around 1 - 3 dB, or more if customer is ok with it, but I would never agree to TD of over 6 - 7 dB even with customer's consent.

[akie_cool]

This certainly isn't acceptable. Given the facts that it's SDH link, I guess it's rather important. Also, it's probably using 128 QAM, and SNR required for such a link is at least 26 dB. Your SNR is 29 dB, so you have a margin of only3 dB. It also means that your threshold degradation is more than 20 dB. Normally, acceptable TD is around 1 - 3 dB, or more if customer is ok with it, but I would never agree to TD of over 6 - 7 dB even with customer's consent.

thanks byja, I really appreciate your respon, but actually im not using SNR approaching, only using BER test result and margin test. I wonder i can find some other reference that explain relationship between interference test's RSL and Microwave link budget RSL. It's 5 GHz system, and 64 QAM modulation.
Anyway, can u show me how to use your method (at least an e-book or e-doc or sort of that, so I can learn much more about microwave transmission in detail and aspects within), how could you know my SNR is 29 dB? Is there any formula to convert it since we're talking about RSL not SNR?. Really, really thanks a lot byja, I really enthusiast learner, and i wonder you can help me.

[byja]

Ok, if you're already using a BER tester and you want to know your link margin, then it's simple: while measuring traffic with a BER tester, gradually reduce output power on the non-interfered side. Do it in steps of 0.5 dB or even less. When you reduce your output power by, let's say X dBs on the other side, and you start noticing errors in transmission, then you know that your link margin is X dBs.
And I suggest you make sure that you can reach the non-interfered side even if the link breaks down, so you can increase the output power back up again.

Based on your info, I guess your link could start having errors at RSL around -49 dBm.

[akie_cool]

Ok, if you're already using a BER tester and you want to know your link margin, then it's simple: while measuring traffic with a BER tester, gradually reduce output power on the non-interfered side. Do it in steps of 0.5 dB or even less. When you reduce your output power by, let's say X dBs on the other side, and you start noticing errors in transmission, then you know that your link margin is X dBs.
And I suggest you make sure that you can reach the non-interfered side even if the link breaks down, so you can increase the output power back up again.

Based on your info, I guess your link could start having errors at RSL around -49 dBm.\
actuallly, im using an attenuator and reduce TX power to the limit that it start producing error to 10^-6, normally it come with -72 dBm before the link is down. But in this case i got -65 dBm before the link is down.
Anyway, could you explain me how to measure interference level whether it's acceptable or not from SNR viewpoint.

Many thanks in advanced byja :loveliness:

[byja]

\
actuallly, im using an attenuator and reduce TX power to the limit that it start producing error to 10^-6, normally it come with -72 dBm before the link is down. But in this case i got -65 dBm before the link is down.

Hold on, if you're having -70 dBm if the other side is not working, then it's highly unlikely that you can have a working link with -65 dBm.
Could it be that you're having some problems with RSSI (RSL measurement) on the radio itself?

[harrypotter]

Or you can simulate first on your lab. I believe that 70dBm is a noise.

[Wizeguy]

\
actuallly, im using an attenuator and reduce TX power to the limit that it start producing error to 10^-6, normally it come with -72 dBm before the link is down. But in this case i got -65 dBm before the link is down.
Anyway, could you explain me how to measure interference level whether it's acceptable or not from SNR viewpoint.

Many thanks in advanced byja :loveliness:

I hope you are using a setup where you actually only attenuate the non-interferer. Incorrect setup would mean that you are attenuating both interferer and non-interferer.
In the end what you measure is just the BER threshold in combination with interference.

Might it be that what you need to test is co-channel interference and or the equipment receiver signature?
This should be possible to get from vendor.
Trick is to have good margin to 10^-6 BER threshold (some 10dB at least) for the non-interferer and gradually introduce an interferer until bit errors occur.
I expect that you will need a directional coupler and adjustable attenuator.
Alternative to adjustable attenuator as byja writes, you can lower the output power on your non-interferer and increase on the interferer.
Make sure to have margin to the receiver 10^-6 BER threshold though.

It will be dependent on equipment type, modulation used etc what to expect.
I am not working with this every day, so I do know what to expect, if 10dB are good or not.
Get the product sheet and compare.