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

[almoqbali36]

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

BR

Dear
We don't have

[Feriko]

Hi,

you have to give more information in order to get helped....

- Try to halt / block 2G cells, if RTWP gets down when halted, it's clearly an IM problem. Then you'll have to check the antenna system, every connector, every passive element, to find where the problem source is. Or you can measure the antenna system with a PIM tester if you have the chance to get one.

- If you halt all cells, 2G and 3G, and RTWP is still high, then you're probably having an external interference. I understand that you have already check that seeing yous comments, so please chech first of all the above point and tell us.

Regards,

David

[RF engineer]

Dear
We don't have

Your U900 taking more user or U2100? and for RTWP you are considering average or maximum in KPI when looking to RTWP? as for my network checked when checked the RTWP increase with HS users increase as this is normal .

BR

[brianm]

1. Make sure you did your frequency refarming correctly including on neighbouring sites. Will be better if you can refarm the whole BSC/cluster
2. Do a footprint optimisation on the surrounding 2G sites to limit over-lapping of signals
3. Reduce excess capacity of 2G sites so that your frequency reuse is greatly reduced
4. Swap around the radio's to check if the interference will move from one sector to the other

[Optimustron]

If you have the UMTS BAND above the GSM BAND is a bad thing, you need to switch the bands because if a single connector/cable/antenna/TRX of GSM is bad you will get IM, by the way you always will have IM but the cuestion is that you have a low level for you technology, for example for UMTS you need to have at most only -130 dBc or -87 dBm because if not you will have high RTWP depending on the level, for LTE you need at most -140 dBc or -97 dBm, by the way you can't remove it by means of filtering because it's in your Rx band then you need to kill that from the source.
Another source of interference is if there is a 800 or 850 Mhz system in your country, because this band have 14 Mhz that overlaps the EGSM band, if that is the case you can use filters and you'll need to put frequencies starting from 904 Mhz at least because if not your RX is desensitized and you'll get high RTWP.
If there is a HIGH BRODCAST TX like TV or FM transmiter or maybe a repeater from another band near to your base station you can get high RTWP too and you don´t will see any interference in your band.
Check if there is a structure of metal near to the antennas, or maybe someting like improper type of paint for your antennas or camouflage in order to hide your antennas, then you can get IM from this kind of passive sources.

Excuse me for this rush and little explanation, However I hope this can help you, best regards,

[zeldalcl]

Hi!
U can think about:
1. Does it has any 850Mhz Network, especially CDMA technology are working.
2. May be equiments issued

BRs!

[brianm]

If you have the UMTS BAND above the GSM BAND is a bad thing, you need to switch the bands because if a single connector/cable/antenna/TRX of GSM is bad you will get IM, by the way you always will have IM but the cuestion is that you have a low level for you technology, for example for UMTS you need to have at most only -130 dBc or -87 dBm because if not you will have high RTWP depending on the level, for LTE you need at most -140 dBc or -97 dBm, by the way you can't remove it by means of filtering because it's in your Rx band then you need to kill that from the source.
Another source of interference is if there is a 800 or 850 Mhz system in your country, because this band have 14 Mhz that overlaps the EGSM band, if that is the case you can use filters and you'll need to put frequencies starting from 904 Mhz at least because if not your RX is desensitized and you'll get high RTWP.
If there is a HIGH BRODCAST TX like TV or FM transmiter or maybe a repeater from another band near to your base station you can get high RTWP too and you don´t will see any interference in your band.
Check if there is a structure of metal near to the antennas, or maybe someting like improper type of paint for your antennas or camouflage in order to hide your antennas, then you can get IM from this kind of passive sources.

Excuse me for this rush and little explanation, However I hope this can help you, best regards,

Can you please explain what you mean by "UMTS above the GSM band" and where the switching is done.

Thanks