A Dual-Band Femtocell Framework for Utilizing Both Licensed and Unlicensed Bands

To increase network capacity, cellular operators have been offloading macrocell traffic to small cells such as femtocells in the licensed band and WiFi hotspots in the unlicensed bands. However, there could be severe interference between macro and femto cells; while WiFi hotspots use the spectrum in a way less efficient than cellular networks. In order to address these problems and further improve cellular capacity, we propose a framework for femtocells to simultaneously access the licensed and unlicensed bands using a single cellular air interface. The framework includes a femtocell radio access technology for the unlicensed band, a strategy to manage the coexistence of the femtocell with the other unlicensed band users and a traffic assignment algorithm over the licensed and unlicensed bands. The framework is guided by our analytical performance models which characterize the coexistence of a femtocell and the other unlicensed band users. The traffic assignment is done to minimize the femto-to-macro interference, while maintaining a required data rate for the femtocell and causing minimal impact to the other unlicensed band users. Results demonstrate that the proposed framework substantially improves the performance of both macrocells and femtocells. Besides, the total throughput of all cellular and non-cellular users are also increased. In addition, the performance degradation caused by the femtocell framework to the other unlicensed band users is similar to that caused in the current approach of building WiFi hotspots to offload cellular traffic. Feilu Liu and Elza Erkip are with ECE Dept., Polytechnic Institute of New York University, Brooklyn, NY 11201, USA. Email: [email protected], [email protected] Erdem Bala and Rui Yang are with InterDigital Communications, 2 Huntington Quadrangle 4th Floor, South Wing, Melville, NY 11747, USA. Email: [email protected], [email protected] This work is supported in part by InterDigital Communications LLC., the New York State Center for Advanced Technology in Telecommunications (CATT) and the Wireless Internet Center for Advanced Technology (WICAT), an NSF Industry/University Cooperative Research Center at Polytechnic Institute of NYU.