I. Introduction
Next generation wireless networks are expected to provide a diverse range of broadband services to meet subscriber demands. Femtocells are a promising direction to improve the performance for in-home users while reducing the load on the cellular (macrocell) network [1]. Femtocells require no infrastructure as they are plug-and-play devices that are connected to the internet backhaul [2]. A main deployment challange is that femtocells operate in the licenced band, and consequently have to share the radio resources and coexist with the cellular network. Solutions proposed to guarantee coexistence range from partitioning the frequency resources between the two networks with closed access, to allowing cellular (macrocell) users to be served by femtocell base stations with open access [1].