High RTWP in many cells

[javierinfante]

hello:
In my network we have many sites with very high RTWP, around -80dbm and even less, the problem is that it happens in all sectors of the site.
I have one site with six sectors U2100 and all six secotrs has the same problem, the RTWP is around -80dbm, so when it happend in all at the same time I can think that it isn't a internal problem, another site the problem is in the U900 and again in all 3 sectors.
We have set an alarm trigger in the U2000 and the value for the RTWP to generate the alarm is -90dbm, to make easier because we have many, so many that -95 is consider acceptable...
I have been checking the possible interferences from near sites, in Google earth, just checking freq and PSC's, but I cant find anything, i also check if the problem could be due to TMA but it happens in sites with and without TMA.
Our network is single RAN with all technologies in one BBU, 2,3,4. We have 2G900, 2G1800, 3G900, 3G2100, LTE800 and LtE2600.
any suggestion, idea??

[tpkj]

Hi javierinfante,

Difficult to answer.
More info is needed.
Is it collocated site with other operators?
What are the antennas configuration (with spliters and TMAs) for each technology?
How many antennas? How they are build (to close each other)?

Could be PIM (passive intermodulation)?

[samuraial]

Try shut down the cells one by one friend and see if there is any improvement in you RTWP values.
If one of those units have problems you will be able to identify it easily.
Also it could be an external interference if any of the sites around has RTWP fluctuation same as your.

B/R

[justdream]

hello:
In my network we have many sites with very high RTWP, around -80dbm and even less, the problem is that it happens in all sectors of the site.
I have one site with six sectors U2100 and all six secotrs has the same problem, the RTWP is around -80dbm, so when it happend in all at the same time I can think that it isn't a internal problem, another site the problem is in the U900 and again in all 3 sectors.
We have set an alarm trigger in the U2000 and the value for the RTWP to generate the alarm is -90dbm, to make easier because we have many, so many that -95 is consider acceptable...
I have been checking the possible interferences from near sites, in Google earth, just checking freq and PSC's, but I cant find anything, i also check if the problem could be due to TMA but it happens in sites with and without TMA.
Our network is single RAN with all technologies in one BBU, 2,3,4. We have 2G900, 2G1800, 3G900, 3G2100, LTE800 and LtE2600.
any suggestion, idea??

As long as this problem happen to many sites and not all sites
could you do some audits to come to the conclusion what's the difference between sites with high RTWP and other sites without?

[shishio]

i think you are having 2 different problems showing up as one
1. G900 interference on your U900 (i suggest that you shut down your G900 cells for 10mins to confirm)
2. External interference on U2100
checking PSC and switching off 3G nbr sites are only helpful when trying to locate DL interference, the situation you are experiencing is UL interference which can be due to 4 major things, high cell load, hardware faults (faulty RRU/connectors/feeder cables), wrong configuration and external interference.so do the below to find out what the issue is
1. check from stats the number of DCH users on the cells 30 or more users and your RTWP might become high, carry out load balance on the cells affected.
2. swap RRU/connectors/feeder cables/Azimuth of impacted cell with another cell that is ok and see if the RTWP will shift to the other cell, if RTWP disappears then you have located the problem.
3. trace the main and diversity Rx of the affected cells from nodeb LMT, if the difference is more than 3db then a hardware fault is very likely.
4. check the configuration you have set for initial access power, number of access retransmissions and ramp step, also check max UE tx power, if these parameters are too high RTWP will be high.
5. carry out a frequency scan of the network to try and locate any external interference.

hope this has been helpful, please give rep

[tpkj]

Still more info needed for advising.
- Is site collocated with other operators?
- Are you using one antenna for all technologies?
- Physical antennas placement - Are antennas behind window, RF transparent…?
- Is it heavy loaded site?
If it is external interferer, increased RSSI (measured on antenna ports) or RTWP (after processing) will be visible on neighbors’ cells as well. The graphical presentation should be correlated in time (15 min granularity).

If it is PIM (passive intermodulation) it could come from your system and also by summing of frequencies from your technologies and co-located operator technologies. Then, you follow the advices from shishio. Turn off 2G or 4G or both to see if RSSI (RTWP) went down to normal value, or better value in case of colocation. You can do online monitoring of RTWP during turning off the other technologies.

If it is a hardware problem (bad connectors, splitters, cables, TMA, Antenna, RRU, RSU..), mostly only one 3G sector is affected, but all carriers (in case of 2G and 4G cosectors).

If it is loaded site, what about transmission on your site and queuing? Are users using 3G: PCH?

[javierinfante]

Hello:
Thanks all for your replies, but I think some ones doesn't apply, for example the intermodulation use to be bigger in one antenna than the another and in my case both antennas have almost the same RTWP value. Also it isnt related to users because the problem is constant, day and night.
Today I was able to check the real hw configuration in the site, and i found that there some combiners, we have GSM 900, UMTS 900, LTE800, LTE2100 GSM 1800, and we use only three antennas, so we need external combiners.
I think I found one problem in one site, because the cell with bad RTWP in U900 is using a combiner together with LTE 800, and I found that the LTE has also interference so Im just waiting for the field engineers to go to the site and to test, bypass the combiner.

[Tcacoilo]

the site is an indoor or an outdoor? Could be the minimum coupling loss that is not guaranteed, basically if you have an indoor you could have too much power in the antenna, and in this type of situation you just need one UE too damage your RTWP

[javierinfante]

hi to all:
I have found the problem, in many cases it was due to wrong attenuation configuration and in another cases was due to actual external interferences.
only two sites are still under investigation because the cause is internal interference from another cells in different RRU, we are searching for crossed calbes, hw problems etc.

[tpkj]

Thank you for the feedback.
Question:
Wrong attenuation configuration was for compesation of TMA?

hi to all:
I have found the problem, in many cases it was due to wrong attenuation configuration and in another cases was due to actual external interferences.
only two sites are still under investigation because the cause is internal interference from another cells in different RRU, we are searching for crossed calbes, hw problems etc.