I have written a tool for SDCCH dimensioning. The number of SDCCH in a cell will be calculated from these input parameters:
+ Number of TRX.
+ Ratio of Location update to calls
+ Ratio of SMS to calls
+ Blocking probability for SDCCH
+ Blocking probability for TCH
+ etc.
The theoretical rule is complex. If you are interested in this tool, give your email.
Nguyen