F3 barred Cell Huawei

[fahmi]

Hi all,

We tryed the barred cell strategy on F3 to limit CS traffic on F3 and only PS traffic via blind HO from F1 and F2 will be carried on F3.

We noticed that for F3 the CELLFACHUEs and CELLPCHUEs come to 0 !

Also increase in PS drop for F3.

Any could explain this.

[hasithamar]

Hi Fahmi,
This seems to be due to an issue in how a UE could decode messages in SIB3 and SIB4. Even though UE moving to CELL-FACH need to read SIB4 to get cell details, most of the UE's unable to correctly decode SIB4. When SIB4 is not correctly decoded, it uses SIB3 and according to SIB3 the F3 cell is idle barred. Therefore when a UE send a message to tranfer UE to CELL-FACH it will try to latch but after few seconds will latch to F1/F2 and send a Cell-Update updating from same sector F1/F2 cells. Therefore there will be no FACH/PCH UE in barred carrier cells.

We had a similar issue and solution adopted was to change strategy as move to F1/F2 based on reselection parameters as below.
For F3 cells add IDLESINTERSEARCH=9 and then,
For F1/F2 cells add IDLEQOFFSET2SN=50 and for F3 cells add IDLEQOFFSET2SN=-50.

[faisaladeem]

Normally SIB4 is not configured and there is an indicator field in SIB3 mentioning that SIB4 is False so the UE shouldn't look for SIB4. This means the same cell selection and reselection settings are used in Idle and connected mode (PCH/FACH). So the SIB4 not being decoded explanation doesn't fit for me.

[kadir]

Hi Fahmi Kardesim

If you remember we faced the same scenario in SA and we have used the same method which hasithamar recommended. I think it is still valid.

take care and enjoy.
kadir

[faisaladeem]

Hi,

We use same strategy of IDLEQOFFSET2SN and I had to search old docs to find out why we chose it long time back, so here's the explanation:

When the cell is barred, it can be barred for idle mode and connected mode independently. If it is barred for both, CELLFACHUEs and CELLPCHUEs will be 0. In this case when the state transition will happen from DCH to FACH, UE has to first reselect another cell (which is not barred) and then send the physical channel reconfiguration response. If this reselection takes longer, the response times out and can result in a drop!

I hope it makes sense.

BR,
Faisal