In a two tier cellular network consisting of conventional macro cells underlaid with home user-deployed femtocells, cross tier interference significantly reduces the average sum throughput of the system. This work considers the downlink cross tier interference problem in Orthogonal Frequency Division Multiple Access (OFDMA) based heterogeneous systems. We analytically derive a frequency reuse pattern for femtocells deployed in macrocells (employing soft frequency reuse scheme) such that the cross tier interference is minimized. The impact of power control factor1 on cross tier interference is also analyzed and system simulation results are presented to ascertain the veracity of the analysis. © 2012 NiCT.