Traditionally, macrocells have been used to provide large area coverage and better handle user mobility in cellular networks. However, as the coverage area increases, more transmitted power is required to provide an acceptable signal quality for cell edge users, which increases the overall BS energy consumption. Recently, femtocells have been deployed to enhance in-building coverage and provide higher data rates. Due to their small coverage area, femtocells require much less transmission power than a macrocell, and hence their BSs consume less energy. However, a deployment with only small cells would require a large number of BSs. This increases the handoff rates of mobile users among adjacent cells and also may degrade the overall energy efficiency of the network. A joint deployment of BSs with different cell sizes is desired. A balance of different cell sizes is required for the most energy-efficient layout [4].