PS IRAT & CS DCR Improvement - U900

[omarGSMUMTS]

coul you share some doc . thank you!

[rumy]

Check the No Cell Found Ratio; it gives you an idea about :
-Wrong GSM Config
-No GSM coverage

Also, you may have restricted International Roamers who do not have access at GSM (this is my case, GSM is used from another operator )

Hope it helped!

[khurrambilal01]

Check the No Cell Found Ratio; it gives you an idea about :
-Wrong GSM Config
-No GSM coverage

Also, you may have restricted International Roamers who do not have access at GSM (this is my case, GSM is used from another operator )


Hope it helped!

Around 30% of attempts end with no GSM cell found for IRAT handover which I can optimize by reducing the target RSSI required threshold for GSM.

Secondly do you mean to say that international roamers which don't have access to GSM because of coverage are all carried over U900?? U900 with same power as G900 has normaly 50% more coverage area.

[litium1000]

If all U900 sites have collocated GSM900, PS IRAT HO makes no sense. U900 provides better coverage and PS user experience than G900. By allowing PS IRAT HO you will just move the drops in GSM.
Pay attention at the number of IRAT neighbors. In Compress Mode, the UE can only measure 8 BCCH's in a gap. It needs 3 measurements per each BCCH for filtering and needs another gap to confirm BSIC. Even if you have less than 8 GSM neighbors it takes 3-5 seconds for a CS IRAT HO. If your IRAT neighbor list is full, for sure it will need more time to measure all BCCH's. If the radio environment is degrading rapidly, you will have a drop before making the IRAT HO.

To have less out of sync radio links , use Ninsync=2, and NoutofSync=200

Also, put a trace in UU interface of a cell, and verify measurement control messages for 2d/2f thresholds. Make sure that the values that you set in SET UINTERRATHOCOV are the ones sent to the mobile. Check for each service: CS only, PS R99, HSDPA and multiRAB. You might have some suprises...

[khurrambilal01]

If all U900 sites have collocated GSM900, PS IRAT HO makes no sense. U900 provides better coverage and PS user experience than G900. By allowing PS IRAT HO you will just move the drops in GSM.
Pay attention at the number of IRAT neighbors. In Compress Mode, the UE can only measure 8 BCCH's in a gap. It needs 3 measurements per each BCCH for filtering and needs another gap to confirm BSIC. Even if you have less than 8 GSM neighbors it takes 3-5 seconds for a CS IRAT HO. If your IRAT neighbor list is full, for sure it will need more time to measure all BCCH's. If the radio environment is degrading rapidly, you will have a drop before making the IRAT HO.

Hi litium1000,

Thanks for the reply, All U900/G900 sites are co-located and i understand U900 coverage is better than G900 but EcNo can get bad not only on U900 borders even near to site because of Pilot pollution in some areas so we need to keep IRAT neighbours and most of IRAT attempts are EcNo based...

Secondly you are right about the time it takes to filter IRAT neighbors for CS but there is no other way possible for CS DCR improvement because once i changed 2D/2F EcNo from -16/-14 to -14/-12 i observed 20% call improvement.

Now I have changed it to -12/-10 and CS DCR is further improved although IRAT per call has increased from 20% to 30%. I have disabled IF HHO for CS so that no users in CS mode can go to U2100 from U900 because it will eventually end with IRAT call and reduce my MOS/increase interference due to compressed mode.

[litium1000]

I have just edited my last post with some sugestions..
It might be a good idea also not to allow inter-freq CS from U2100 to U900, and send them directly to IRAT. This could help in your scenario if you have many CS interfreq U2100 to U900, because this type of calls only be counted as drops in U900..they are established in U2100 cells, and possibly dropped in U900 ). In calculating DCR in U900 you count drops/established in U900 band

[khurrambilal01]

I have just edited my last post with some sugestions..
It might be a good idea also not to allow inter-freq CS from U2100 to U900, and send them directly to IRAT. This could help in your scenario if you have many CS interfreq U2100 to U900, because this type of calls only be counted as drops in U900..they are established in U2100 cells, and possibly dropped in U900 ). In calculating DCR in U900 you count drops/established in U900 band

Normally the dropped call during handover phase are counted on source cell that why we always normally monitor outgoing handovers.

Changing In/Out sync Indication timers seems not right to me because instead of resolving the problem we are trying to hide it by changing timers that too very high values.

[litium1000]

Normally the dropped call during handover phase are counted on source cell that why we always normally monitor outgoing handovers.

Changing In/Out sync Indication timers seems not right to me because instead of resolving the problem we are trying to hide it by changing timers that too very high values.

- I was talking about overall CS drop call rate in U900 band
-Changing InSync/Out Sync makes no difference for PS. For sure, even with this timers, user experience will be far better than GSM. You might have some problems with CS..but not necessary.

In my opinion, your strategy is your problem. It really makes no sense making HO from U900 to G900 if you have continuous layers. If you have no choice in changing the strategy, try to be more aggressive at cell level. Find worst cells, use agressive cell level EcNo/RSCP interRAT parameters, while trying to improve EcNo in the U900 cells.

[khurrambilal01]

Hi litium1000,
If we keep users to U900 layer and don't push them to G900/1800 even when EcNo/RSCP is bad, KPIs for U900 are going to be too bad and we have targets
Secondly U900 load is already high so keeping CS users when the coverage (EcNo) isn't good will drop KPIs as well as increase traffic.

We have to balance G900/1800, U2100 and U900 KPIs and traffic as well as provide coverage to new users which are not served by U2100...

Changing Insyn/Outsync timers will affect CS only that's true but changing timers will reduce call drops in statistics not on-ground.... (Users will still face dropped calls and instead of waiting for too long they will finish the call themselves)

[litium1000]

You can try to offload U900 to U2100 through idle reselection (if you haven't done it by now). Prioritize reselection to 2100 Band from U900 and G900. Keep idle and connected UE's as much as possible in U2100. Do not allow CS interfreq from U2100 to U900, send the calls directly to IRAT. If U2100 becomes overloaded, expand 2nd carrier (probably you have more spectrum available in 2100 than 900 band).

Good luck!