PDA

View Full Version : Same BCCH



simmus0300
2010-08-19, 11:46 PM
There are three cells A,B,C.The neighbour relation of cell A is defined with cell B & C.cells B & C have same BCCH but different BSIC.My question is whether Handover of A with B & C will takes place succesifully or not.?if not why ?

Optim
2010-08-20, 02:01 AM
Of course there is no problem to define 2 target cells with same BCCH and different BSIC, because the MS on MMR (mobile measurement report) will report two same BCCH but with different BSIC and the BSC sent the handover command for target with high level. and to avoid any problem for decoding BCCH you can play on TSC, by default is equal to BCC.

pathloss
2010-08-20, 02:46 AM
This will only work correctly, as long as there is no co-channel interference with cell B&C. If there are interfered areas, the handovers won't work correctly, as the mobile station will have problems to decode BSIC. Result is that Handovers are likely to fail.

For my opinion it's bad planning when you have cells with same BCCH at co-located sites. Even if the sector with cell B on Site B and the sector with cell C on site C are facing in opposite direction. There is still the possibility, that the antenna back loop creates interference.

danikd
2010-08-20, 04:57 AM
This will only work correctly, as long as there is no co-channel interference with cell B&C. If there are interfered areas, the handovers won't work correctly, as the mobile station will have problems to decode BSIC. Result is that Handovers are likely to fail.

For my opinion it's bad planning when you have cells with same BCCH at co-located sites. Even if the sector with cell B on Site B and the sector with cell C on site C are facing in opposite direction. There is still the possibility, that the antenna back loop creates interference.


Agreed with Pathloss!!!

It seems that there is a bad frequency allocation here.

The HO performance of such configuration is fully depends on how far B and C located from each other and do they have signal overlapping within the coverage area of cell A.

Even if you have different BSIC allocated for B and C, this does not promise separation. The mobiles in active mode decoding BSICs of neighboring cells with pretty low repetition rate i.e. 5-30 seconds. It is depends on how many neighbors defined in cell. But the BCCH frequency of the neighbor cell measured with very high repetition rate few times in second. Once mobile does not able to decode BSIC for specific BCCH it continues to apply up to 30 seconds the latest measure BSIC for neighboring BCCH frequency. This may lead to HO triggering to the wrong target cell in situation when mobile travelling from cell B to C via cell A. Mobile may report BCCH/BSIC of cell B, while it should be BCCH/BSIC of cell C. Mobile just can not decode BSIC of Cell C due to low C/I between B and C within the coverage of cell A.
As result BSC triggering HO to cell B, but it failed, since the strongest neighbor signal was from C, but mobile was forwarded to B due to this effect.

This effect is well known and called SHADOWING (cell B put the shadow on cell C and vice versa).
In order to avoid such collisions, you may apply triangulation rules (restriction between second tier neighboring cells) for you frequency planning tool, or you may add those restrictions for all currently co-BCCH cells relations (more strict restrictions). The resulted frequency allocation plan will be SHADOW free!!!

D33T0X
2010-08-20, 06:09 AM
Bad planning, HO failures will most probably occur due to interference. There's a slight possibility that all will be OK. Keep an eye on your network KPI's.

syeddawer
2010-08-20, 09:59 PM
As long as you can keep both B and C pointing in different directions, it will not be safe. Acceptable to say the least.

Otherwise, as people have suggested here, it would create a mess.

Example:
HO command will go for server B, but UE tries to camp on server C.

BR..
D

guruvai
2010-10-06, 11:54 PM
From my practical experience, I faced problem with handover (handover failure) even for same BCCH in the neighbor. Because of wrong BCIS decoding MS can't locate itself correctly and cause to handover failure. So, i suggest not to put same BCCH in the BA list if you have enough freq to do so.