A Hierarchical SDN Architecture for Ultra-Dense Millimeter-Wave Cellular Networks

Abstract

To cope with the tremendous growth in mobile data traffic, ultra-dense networks (UDNs) will be deployed in the future cellular network. Meanwhile, the enormous amount of available spectrum in millimeter-wave (mmWave) bands can be also exploited to increase the wireless link capacity. In accordance with these trends, this article introduces a novel hierarchical software-defined networking (SDN) architecture to facilitate the deployment of UDNs with both microwave base stations and mmWave access points. Aimed at reducing the cost of computational complexity and signaling overhead, the novel SDN architecture employs a semi-distributed design approach by configuring two levels of controllers: the centralized superior SDN controller and the localized subordinate SDN controller. Some practical challenges posed by the characteristics of mmWave transmissions, such as high propagation loss, channel blockage, and directional beamforming, are also discussed. To deal with such challenges, we then propose several important network operations for the hierarchical SDN, including dynamic subordinate SDN management, mobility management, and user-centric design. We finally provide simulation results to demonstrate the performance advantages of our proposals.