You've decided to represent each transmitter in every cell by a finite domain variable (of type IlcIntVar) which takes its value from the set of available channel numbers.

Distance constraints are expressed in a deterministic way by using the predefined symbolic constraint IloAbs. This deterministic expression is important with respect to the complexity of the algorithm, since the constraint IloAbs(X-Y) >= D replaces the disjunction of the two constraints X-Y >= D and Y-X >= D. This principle--of using a symbolic constraint instead of the disjunction of two or more constraints--is one that can help you reduce the complexity of other problems as well.

This problem, for which the data set (namely, the distance matrix) is rather small, translates into a quite large number of constraints--more than 8000.