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chiku
2010-07-10, 10:43 PM
In one of market we are facing gsm -cdma interference.As we have gsm scanner and gsm phones,our scanner and phones interprets some gsm channel of our band and gives values.it shows rx level around 80 to 105 for those channel .this all testing done by locking all our gsm site.there is no other gsm operator working on same band.when we turned off some of cdma site of other operator rx-lev for channel which we were decoding went down.also when we unlock our sites and did testing in good rx-lev our rx-qual is band and there is no co channel and adjacent channel interference.also through spectrum analyser we did testing but we could not finf any gsm channel of 200 khz at that spot but ya same level of cdma channel were found.
I had same issue when i was working with one operator long back but it was case we had cut to cut band with cdma operator and we use to put band pass filter but here it seems it overlaps.also how much is bandwidth for cdma channel?and how can we counteract those thing?

coursekec
2010-07-10, 10:56 PM
i m also facing similar sort of problems...optimization gurus please help

rosan
2010-07-12, 02:36 PM
Dear Chiku,

what is the DL band that CDMA operator is using?
normally there is no chance that CDMA DL interfere the GSM DL because the bands are far apart, but the possibility is CDMA DL interfere the GSM UL. It is not your case though.
Make sure any 3 order IM from that CDMA operator falls in your DL band.

Thanks.

Mohamed Jaboura
2010-07-12, 06:13 PM
I'm Also facing this problem, mainly this seems to be critical if the GSM network is E-GSM and the highest CDMA carrier is for EVDO. EVDO uses full power transmission unlike CDMA1X. May be you give us more details about the frequency bands carrier numbers KPIs and vendor and BTS model. May be I can help if I get more details about the scan results and any more useful information

chiku
2010-07-13, 12:28 PM
can you elobrate how cdma channel and gsm channel in ul and dl are allocated .So do u think because of that our UE might transmitt with high power all time ???


Dear Chiku,

what is the DL band that CDMA operator is using?
normally there is no chance that CDMA DL interfere the GSM DL because the bands are far apart, but the possibility is CDMA DL interfere the GSM UL. It is not your case though.
Make sure any 3 order IM from that CDMA operator falls in your DL band.

Thanks.

rosan
2010-07-13, 05:56 PM
Hi,there is a operator in E-GSM thier UL is 880 to 885 MHz, they get interference from one CDMA operators DL carrier which ends at 978.5 MHz (remember the CDMA2000 carrier BW is 1.25 MHz). In the places where sites are closer the CDMA interferes GSM eventhough its not exactly in the same band. 2.5 MHz is the recommened seperation between CDMA DL and GSM UL.

d0000h
2010-07-16, 02:27 AM
I have personally seen issues between DL GSM 850 and UL UMTS 1900 but that was when they were combined on the same line/antenna (both tech were ours).

Is this happening everywhere or only a specific site or two?
Where it happens, what is the distance from where you are measuring the signal to the CDMA tower?

Probably either their TX is "bad" (spurious emissions) or there is intermod due to a combiner, bad jumper/antenna etc. Try having them swap lines so they TX using the other line. In this case is it the same antenna or different antenna? Even if same antenna, different port should be OK as a test as one port could be bad and one could be good.

If still bad, then assume bad TX and have them install a filter or swap the TX with a radio from a site that does NOT show this problem. Perhaps even a different sector of the same site.

Yes we work with other carriers to help with solutions, but in the end (in Canada) if another carrier is causing problems within our band, it is their responsibility to find a solution.

telwind
2010-07-16, 11:28 AM
Some thing I can share with you.

I've faced this and took long time to find and finally we rectify it. It is hard to explain some words here. it is said that normally is is relate to the close proximity of the CDMA downlink and GSM uplink frequency bands.

If this, it leads to interference in the GSM receiver, thereby decreasing its sensitivity and resulting in dropped calls or can't make calls. The impact of this would be a dramatic and unacceptable degradation of the sensitivity of the GSM receiver. like you see GSM Rxlev -80dBm but cant make call successful. Spurious emissions are caused by unwanted transmitter effects; CDMA transmitters can generate both discrete (harmonics, intermodulation products) and wideband signals that fall outside the transmit band. If these fall within the GSM receive band, they manifest as wideband noise and raise the noise floor of the receiver.
If the strength of the signal into the GSM receiver is higher than a certain level (called as the ‘blocking’ level)), it generates intermodulation products that can lead to interference.

By use spectrum analyser, we cant find spurious emission much. But we can see the resulted interference in the system by IOI or similar in some vendors like ********, E*******, etc. it is high which cells have problem with this kind of interference. by shutdown the CDMA site then IOI will reduce. eay way to find the CDMA site is the CDMA site close to GSM site and whose antenna face to GSM antenna.

To fix the problem, some ways can think and do:
- Change of antenna height or even direction. this is difficult due to effect to your expected coverage footprint.
- reconfig the BCCH/FCH frequency, GSM site have problem should use far GSM channel from CDMA. this is lightly difficult.
- Installation of filters both the CDMA downlink (your competitor) and GSM uplink (your site). this causes some dB loss.

You can combine all of them if possible.

Hope this will help.

d0000h
2010-07-17, 12:39 AM
Makes sense Telwind, however I believe the issue stated with DL GSM, DL CDMA. It was stated when the CDMA was powered down, the RSSI level the phone and scanner measured decreased.