Heterogeneous mobile networks, HMNs, with flexible spectrum use, densified cell deployment, and multi-layer multiple types of radio access technologies, are expected to be key to meeting the 1000 times increase of mobile data traffic in 2020 and beyond. The increasing complexity in HMNs renders the control and coordination of networks a challenging task. The control frameworks of current cellular networks, which were previously designed for sparse network deployment, hit the wall for HMNs. HMNs need good separation of control and data planes, and call for novel control methods to handle the highly complex dynamics therein. In this article, we first briefly review the control planes of 2G to 4G cellular networks, and then identify their constraints to support HMNs. We analyze the complexity in HMNs and examine enabling control technologies for HMNs. We believe new thinking is needed for efficient control of HMNs. SDN is a promising technology to solve complex control problems in the Internet. Principle-based control methods applied in SDN are promising to solve control problems in HMNs. Several SDN approaches have been proposed for mobile networks. However, most of them are targeted at mobile core networks. We propose an SDNbased control framework named SoftMobile to coordinate complex radio access in HMNs. The main features of SoftMobile are low-layer abstraction, separation of control and data planes, and network-wide high-layer programmable control. Important research problems in SDN for mobile networks are highlighted. We believe SDN for mobile networks will be the controlling evolution of future HMNs.
- software defined network
- radio access network
- heterogeneous mobile networks
- architecture design