interference in U900

[almoqbali36]

Dear All
I am facing some issue in our network, we have Single RAN Huawei equipment and we start using U900 on EGSM band.
but once we put the sites on AIR we found High RTWP in U900. we checked the spectrum by analyzer and it was clear. is there any possibility the interference is coming from the equipment. we have a single RAN system we connect 2G and 3G U900 with same cabinet.



BR
Rashid

[vaampeere]

Hi Rashid,Best way to check is get the frequencies listed and make a LMT trace.Also 1) what times do you face the RTWP in the network?.2) Is it a random trend or at some particular time intervals?.3) Are you using filters for both bands? 4) Are you using any TMA's?

[almoqbali36]

dear
What you mean filters??
it is continues. we are using same antenna and using single MRFU for both GSM and UMTS. no TMA is used.

[tremalnike]

Intermodulations?You may do some calculations for IM products

[almoqbali36]

Dear
What you mean IM product? If you mean intermodulation, how it is done?

[tremalnike]

Use this http://www3.telus.net/PassiveRF/ or any IM calcualtor.Enter GSM carriers TX frequencies in "TX" , UMTS UL freq in RX and check for "hit"

[s52d]

Intermodulation happens if there is some nonlinearity (it allways is...).
If TX signals are changed depending on their amplitude (distorsion), you can get all possible combination of frequencies.
Good side: amplitude lowers with IMD degree.

example: f1,f2 ... fi are TX signals.
fimd = n1*f1 + n2*f2 + n3*f3 .... ni*fi
where ni is any integer.

IMD degree is sum ob absolute values of Ni.
As we normally oibserve only 2,3,4,5 degrees, it is simple.

As GSM 900 uses 45 MHz duplex distance, two signals with 22.5 MHz can generate interfernce. (on higher RX).
if you use GSM on EGSM band and WCDMA 900 on upper GSM band, then you might have 22.5 MHz difference and interference.

It is common when cositing GSM900 of two operators. As GSM is 35 MHz wide, 22.5 MHz difference is likely.
Most common sollution is to replace antenna, sometimes water in cable/connectors made then nonlinear.

On antennas: it is our procurement demanding cheaper and cheaper antennas, so even reputable vendors can not use high quality
material. So antennas have to be replaced more often, and some time has to be spend on finding foulty units.

br
s52d

[patek1968]

Dear All
I am facing some issue in our network, we have Single RAN Huawei equipment and we start using U900 on EGSM band.
but once we put the sites on AIR we found High RTWP in U900. we checked the spectrum by analyzer and it was clear. is there any possibility the interference is coming from the equipment. we have a single RAN system we connect 2G and 3G U900 with same cabinet.

BR
Rashid

Your 2G and U900 share common antenna? If so, try to check 2G BTS power might have something to do with the power mismatch in U900. Check also your uplink congestion in M2000 using DSP UCELLCHK and check Cell Uu Uplink congestion state. This was common in U900 that co-locate with GSM. Hope you find it useful. Thanks

[vaampeere]

dear
What you mean filters??
it is continues. we are using same antenna and using single MRFU for both GSM and UMTS. no TMA is used.

Sorry for the dealy.If its the same antenna then no need for any filters.IM could be the real cause due to any internal fault or that of Hardware.

[RF engineer]

Dear All
I am facing some issue in our network, we have Single RAN Huawei equipment and we start using U900 on EGSM band.
but once we put the sites on AIR we found High RTWP in U900. we checked the spectrum by analyzer and it was clear. is there any possibility the interference is coming from the equipment. we have a single RAN system we connect 2G and 3G U900 with same cabinet.



BR
Rashid

Do you have CDMA 850 . if yes as vaampeere said you need filter due to intermodulation.

BR