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Muhammad Imran Rafique
2011-12-31, 05:21 PM
Hi All,

(STC project, E******* Section)
We are facing a problem in terms of low IRAT cell reselection in our network. When we checked in per cell relation stats we found IRAT handover is OK while IRAT cell reselection is poor. All relevant parameters are same what can be the reason? I would like to add onething here that as per e******* documents its not mentioned anywhere that congestion in target cell (for IRAT CC) is any reason for poor IRAT CC performance.

BTW our target cells in 2G are not congested in PS/CS. There is no external interference on 2G cells.


BR//
Imran Rafiq
+966 53 420 35 17

jayk
2012-01-01, 08:28 AM
Do you have figures of your IRAT Cell Re-selection, means percentage of IRAT ReSelection Success Rate?

Muhammad Imran Rafique
2012-01-01, 02:53 PM
There are certain relations where IRAT handover success rate is above 95% but their IRAT CC (cell change) is less than 20%. The IRAT CC attempt is also very high above 500/day.

BR//
Imran

byron
2012-01-02, 03:16 AM
Hi,

Your IRAT cell reselection could be poor due to missing or incorrect definitions on your GSM cell. Ensure that the correct UMFI, SPRIO=YES, QSI=7 etc: If for E*******, check out sample commands below.



RLSUC:CELL=gsmcellx,FDDMRR=1,QSC=15,QSCI=1,QSI=7,SPRIO=YES,FDDQMIN=6,FDDQOFF=0,FDDRSCPMIN=6,FDDQMINOFF=0;



RLUMC:CELL=gsmcellx,ADD,UMFI=UARFCN-SC-DIV;

RLNRI:CELL=gsmcellx,CELLR=3GNeighborcell,SINGLE;

rezapa
2012-01-02, 04:36 PM
Hi Imran,
Of course cell reselection has nothing to do with congestion, and we have no statistics of that. I think your issue is regarding "IRAT cell change", which is different than simple reselection (although criteria of choosing target cell is the same). Cell change depends on availability of PS channels in target cell. So if the target cell is not able to assign PS resources, MS will try to return to 3G cell and it will be counted as a IRAT Cell Change Failure. This is from ALEX:
"If the UE fails to access the GSM/GPRS cell and returns to the old channel. A RADIO LINK RESTORE INDICATION is sent from RBS to the SRNC to indicate that the UE has returned to the old channel, then the UE will send a CELL CHANGE ORDER FROM UTRAN FAILURE message to the SRNC. The Inter-Rat Handover Evaluation is informed about the failure."
One strange thing I experienced is that IRAT CC Sucess rate was about 85% when we had only 1 3G carrier. After launching the 2nd carrier, IRAT CC sucess rate increased to over 90%. So it seemed to me that quality of 3G cell also affects the IRAT CC KPI (How? why?).
Regards,
Reza

Optim
2012-01-02, 11:00 PM
Hello Reza,

If u launch the second carrier then you are increasing the IFHO and then ITA % will get less...if IRAT attempt is less, probability to get fail is less and the success is increase...

of course qauality in 3G cell is affecting the IRAT %..as the IRAt from 3G to 2G is trigged by 2nd RSCP and EcIo threshold.

BR,

rezapa
2012-01-03, 01:43 AM
Hi Optim, Thanks for your reply. As I understand, quality of 3G cell affects 'when' the IRAT CC/Ho is triggered. So I totally agree that after introduction of 2nd carrier, 3G coverage would increase, hence IRAT events happen farther away from 3G cells. The success, however, mainly depends on cleanness of frequency of destination 2G cell (did the MS correctly decode BCCH/BSIC? Is 2G frequency clean? In case of Cell Change, does 2G cell have PS resources to assign?). So I still persist on my question of why IRAT CC success increased abruptly?
In our case, we don't have a criteria on RSCP (only EcNo is considered to determine 3G cell range). After 2nd carrier, 3G drops decreased, traffic remained the same, IRAT CC attempt remained the same, IRAT CC sucess increased. I have doubts why traffic didn't increase too!
Reza