A method for controlling the aggregate interference of a secondary system (10) in a cognitive radio network comprises the steps of computing the power density (Pd,i), footprint (Afoot,i) and service area (Ai) for each of the cells (100) of the secondary system (10) that satisfy the interference constraint at a given point (P) in a primary system (50); summing the power densities (Pd,i) for all cells (100) for the point (P); and using the sum of the power density at the point (P) to decide which power level a new secondary system (10) user is allowed to use in a given cell (100). A system for performing such a method is also disclosed.