According to the GSM standard 05.02, “for broadcast and common control channels, the TSC must be equal to the BCC.”
In some configurations, to use TSC different from BCC on TCH and SDCCH channels situated in TS0 would allow to avoid random access interference. For example, a random access sent on TCH on TS0 (for handover) could be detected as valid on the RACH. Apparently, this could happen when frequency channels in use in the TS0 in non-BCCH TRX are quite close to BCCH frequency channel (400 kHz or 600 kHz spacing).
This feature removes the TRX specific constraint: TSC = BCC. Exception for this limitation is BCCH and PBCCH TRXs and also Base Band hopping cell (or Base band hopping layer in IUO case).
This would lead to following network quality improvements:
less ghost CHANNEL REQUEST on RACH => better SDCCH efficiency
less misbehavior on TS 0 during handovers.
my general question:
can we use TSC different from BCC on TCH and SDCCH channels situated in TS0 for all cells?
The BCC is defined per cell, not per TRX, not per TS.
a Handover Access towards cell B can be decoded as a Channel Request in cell C only if :
a) “target” TCH frequency (B) is the same as the BCCH frequency of C
b) target cell BCC in (B) is the same as the BCC in (C).
Whether or not the target TCH is on TS0 doesn’t really matter, unless the cells B & C are synchronized. But Sync Cells usually belong to the same BTS, and I doubt intra-BTS cells are going to use same frequencies 🙂
Now, if adjacent frequencies… frankly, ok, it *could* happen (as in “anything* could happen). But not much. Not much at all…
In my previous message, when I said “BCC”, I actually meant “TSC”. Replace all instances of BCC by TSC… it is the couple (freq, TSC) that shall not be repeated among cells nearby each others.
Anyway, the main questions still remains :
– why is there a relationship between BCC and TSC ?
– why only on TS0 ? since cells are not sync, the TS5 of a cell might very well fall inside the TS0 of another cell.