Q: BCCH interference

[peanut]

Gents,

Can the MS distinguish the signal of two BTS using the same BCCH but different BSIC?

Thanks,i

[fantominox]

Hi,
of course, MS can distinguish, depends on level of interference(C/I) in place of measurements and difference between BSICs on bit level (BCC).


BR
Fantominox

[firstmaxim]

The concept of BSIC is introduced to help the MS in the connected mode to read the physical layer cell ID (it does not read the BCCH of the neighbors, during the connected mode). The signal strength of the neighbors is assigned to the BSIC (read from the SCH during the idle frame), and sent as measurement reports to the network on the SACCH channel So, coming back to your question, the MS distinguishes BTSs using the same BCCH by its BSIC.

[Bili]

I think this 2 sites have same BCC please check & be sure about BCC diffrence.

[maahsan]

MS stores BSIC for each BCCH and it is not updated as frequently as BCCH is scanned so if a cell has two neighbors with same BCCH and different BSIC there is a possibility of wrong handover decision.

[lamagica]

so what would happens if ms in connected mode and it reads two different frequency neighbor with the same BSIC?

[maahsan]

This is normal and MS will have no difficulty distinguishing between these two neighbours.

[lamagica]

so it wont be have any bad effect, if some near cells / adjacencies having the same bsic?

[maahsan]

It is the combination of Co-BCCH/Co-BSIC (also Co-BCCH/Co-BCC) that creates the problem. If the BCCH are different than BSIC doesn't make any difference.

[lamagica]

lets continue our discussion about frequency :)
maahsan, the gsm networks i'm handling right now have a very limited frequency in 900Mhz band. so, its very difficult to assign the frequency so there wont be any adjacent BCCH, from your experience is adjacent bcch have a big impact on the radio quality?

[maahsan]

Adjacent is always better than Co-BCCH. However you should avoid assigning Co/Adj-BCCH to cells that are overlapping too much (serving the same area).
Do you have access to some AFP tool?

[lamagica]

maahsan, what do you mean by AFP tool?

[huawrx]

MS stores BSIC for each BCCH and it is not updated as frequently as BCCH is scanned so if a cell has two neighbors with same BCCH and different BSIC there is a possibility of wrong handover decision.
I agree with you, normally drops due to HO is affected by it, it is beter change BCCH for reduce interference.

[maahsan]

AFP = Automatic Frequency Planning

There are two categories of AFP tools, one uses coverage prediction to generate interference matrix e.g., ILSA (part of aicom enterprise suite) and the other uses MR (measurment reports) to generate interference matrix e.g., Optimi AFP, Actix CellOpt AFP. The later category of tools are considered to be more accurate as their input is based in real data instead of predicted data whose accuracy depends further on accuracy of maps and model being used.

[lamagica]

we use planet for coverage prediction, but unfortunately i dont have the access or the expertise to use it :(

[peanut]

Adjacent is always better than Co-BCCH. However you should avoid assigning Co/Adj-BCCH to cells that are overlapping too much (serving the same area).
Do you have access to some AFP tool?

To emphazise on machaan post:

An optimal frequency plan require a mimimum of interference ratio to be respected (Co-Channel, Adjacent-Channel), GSM spec 05.05 has defined:
Co Channel Interference: C/I = 9 dB
Adjacent Channel (200 Khz) Interference: C/I = -9 dB
Adjacent Channel (400 Khz) Interference: C/I = -41 dB

based on the bellow, you can see that the impact of an adjacent channel interference is less that a cochannel interference, this is why we have a greater C/I

A rule of Thumb
Avoid adjacent channel on:

same cell
co sitted cell
cells with high overlapping

regards,

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