Roaming border problem

Hi,

A mobile phone is going to roam only if it has lost its home coverage, or if the neighbor cell from the other country provides a better coverage. The second possibility would be an inter PLMN reselection, and I’m not sure whether it’s possible or not 🙂 Anyway, we can try to avoid reselection.

So why are your subscribers loosing your coverage ?

1/ BTS is down
2/ Wrong cell selection / reselection settings (check RXLEV ACCESS MIN value, should be around -110dBm at country boarder, increase the CELL RESELECT HYSTERESIS up to 10 or more dB)
Also, you might want to increase the Cell Reselect Offset. Perhaps the other operator have increased its CRO so much that their cells pull your MS’s out of home PLMN. As I said before, that would be an interPLMN reselection, and I don’t know if it exists or not…
Or perhaps I did, but then I forgot 🙂

Have you perform a drivetest in this area ?

I assume you declared the neighbor cell (from other country) as a proper neighbor ? If yes, during a drive test, you can see why a MS would leave your home coverage. Contact the customers that complain, go to their house, and see why it’s happening to them.

RACH,

You should explain a bit more if you want more help.

Dear, Pix and RASH!
There is no notion “PLMN reselection”. There is only new-PLMN selection procedure, that triggered by overall loss of previous PLMN coverage (no suitable cells in previous (i.e. home) PLMN).
After new-PLMN selection in different country PLMN,MS is staying in that PLMN until any suitable cell exists in it, even the home network is already available.
RASH, you can prevent this problem by preventing your subscriber to register in that PLMN, or by expanding home PLMN coverage.

Hello Pan,

I wrote an answer, but it didn’t get published..

Still, something is not clear…

There are inter PLMN Handovers which are possible, and so are inter PLMN cell reselections. If both handovers and reselections are possible, it means that you shouldn’t wait for a total loss of coverage before going to another PLMN… In 3GPP, it says that a loss of coverage is one reason for triggering an interplmn reselection. But if the interplmn neighbor is described in the SI5/SI2 messages, wouldn’t the MS be tempted to do the reselection?

That’s an open point, I’m still looking for the answer..

Yes, paraHO, we discussed this problem earlier 🙂
Dear, RASH! I heard about border gateway in relationship GPRS only. How will you intend to use this network element in CS-network?
As to HPLMN searching timer, then it is useless in your case (when Visited PLMN is other country PLMN). MS take HPLMN timer in account only in its Home country.
Dear, Pix!
There is an inter-MSC handover – not inter-PLMN. The cell reselection procedure is applied only to cells which belong to selected PLMN (i.e. MS will check MCC-MNC this cell before using it as cell reselection candidate).
with BR, Pan.

Yes, Pix,
I really found out the mention about this feature in 22.129 since REL 4. As in rel-7 said it is an optional feature to implement and as I seemed, this feature not designed completely up to rel 7 anyway, because there are many “open points” on Inter-operator Handover recognized in 22.129.