Determining the Number of RNCs

As previously mentioned, the capacity of an RNC is typically limited by
some or all of the following factors:
■ Total Erlangs
■ Total BHCA
■ Total Iub interface capacity (Mbps)
■ Total Iur interface capacity (Mbps)
■ Total Iu interface capacity (Mbps)
■ Total switching capacity (Mbps)
■ Total number of controlled base stations
■ Total number of RF carriers
In most cases, one will find that the Iub interface capacity is likely to be
the limiting factor. For example, a typical Iub limit for an RNC is between
150 Mbps and 200 Mbps. The same RNC might well have a limit of 500 or
more RF carriers (that is, cells if only one carrier per cell). Given that we
might expect a cell to support 500 Kbps to 1 Mbps, it is clear that the number
of RNCs is likely to be driven by the total Iub interface bandwidth than
the other factors. Of course, once we determine the number of RNCs based
on the Iub bandwidth required, we need to validate that no other RNC
dimensioning limits have been exceeded. If they have been exceeded, then
additional RNC capacity needs to be added according to the most constraining
factor. That, however, would be an uncommon situation.