selection of SDCCH/8 or SDCCH/4 signalling channels depending on behavior of your subscribers.
Moustly SDCCH/4 could be enought for 1 TRX cell. Moustly SDCCH/8 could be enought for 2 and 3 TRX cell. Moustly 2xSDCCH/8 could be enought for 4 TRX cell. But in special cases you must add the next SDCCH due to blocking (LAC border, social event complex..). Very usefull if feature caled as TCH/SDCCH channel. Check yor SDCCH blocking from counters. If you have blocking for particular cell > 1% (or 2 or 5 – depends up to you) then add SDCCH to this cell.