Two-tier femto-macro wireless networks: Technical issues and future trends

Femto/small cells have been considered a promising technology in wireless communications for extending indoor-service coverage and for improving overall network capacity. Two-tier networks — where the current cellular networks, i.e., macrocells, overlap with a large number of randomly distributed femtocells — can potentially bring significant benefits to spectral utilization and system enhancement. In this article, we provide an overview of two-tier femto-macro cellular networks, together with insight into recent research activities and results. We focus on the following technical topics relating to two-tier femtocell-macro cell networks: spectrum allocation, interference management, and access control. Other key issues, such as backhaul, user mobility, and energy efficiency, are also discussed. Finally, we describe developing trends relating to femtocells, and conclude with describing possible future research directions.