Is it possible to find an optimization to the following theoretical case?
Given is a cellular (phone) system with hexagonal cells, where the volume of transmission and the size of the cells are designed such that the same band (frequency) can be used by two cells that don't share a common edge. It can be assumed that the collection range of bands (frequencies) can be divided into $n$ equal groups of band (frequencies) ranges in order to maximize the number of cellular calls that can be made in parallel in a given cell.
How can we find $n$?
I thought about the clustering of frequencies, i.e, a function $\{f_1,...,f_n\}$, and then, using the given topology (hexagonal), construct the clustering using the intuition that a cluster of size $n$ can be constructed if and only if $n=i^2+j^2+ij$. However, I think I am going in the wrong direction since I am not sure how to handle that the "same band (frequency) can be used by two cells that don't share a common edge". Here I am lost.
Is there an efficient solution to that?
A relevant picture: