Femtocells have been recently proposed as a potential good solution to increase not only indoor radio coverage, but also system capacity. In this paper, a framework for radio coverage prediction and system level simulation for WiMAX macrocell/femtocell scenarios is presented. Furthermore, the feasibility of the co-channel deployment of WiMAX femtocell in an existing WiMAX macrocell network is investigated, and a method for interference avoidance based on DFP (dynamic frequency planning) is proposed. The resulting impact of DFP in a macrocell/femtocell scenario compared with other frequency assignment strategies is analyzed. Experimental evaluations carried out using our framework show the boost in the system capacity when using DFP and femtocells.