The femtocell base station is a low power and low cost small base station in the customer premise. It connects to the core network via cable, DSL or similar backhaul technology. In this paper, we focus on how received signal quality can be improved by deploying femtocell base stations in a WiMAX system. We propose a suburban femtocell model to analyze the potential improvement on the SINR when using different channel assignment schemes and different deployment densities of femtocell base stations within a macrocell. The simulation results show that we can enhance SINR by deploying large number of femtocell base stations within macrocells, and the Least-Interfered-First (LIF) scheme we proposed can be used to significantly reduce the co-channel interference induced by neighboring femtocell base stations.