Adaptive Cell Zooming and Sleeping for Green Heterogeneous Ultradense Networks

Abstract

With the increasingly dense-deployed small cells, the heterogeneous ultradense network (H-UDN) now faces new challenges. In order to fulfill user traffic demand and improve network energy efficiency in H-UDNs, this paper researches on the adaptive cell zooming scheme to achieve the optimized user association through adjusting cell coverages. Then, the cell sleeping scheme is further applied to turn off light traffic load cells for base station (BS) power saving. We define the cell zooming factor (CZF) to express cell coverage, which is derived as a closed-form expression with the relationship of small cell and macro cell densities. The user association probability with one typical cell is also derived, where the probability is related with both the transmission power and CZF. We apply the game theory to optimize the CZF based on reduction of area power consumption. Based on the fact that users are encouraged to associate with small cells to reduce transmission power consumptions, the small cell sleeping scheme is further applied to improve the network energy efficiency, while the sleeping small cell users could be offloaded to macro cells. The sleeping probability is defined and derived with influences of different sleeping thresholds. We optimize the threshold with maximized energy saving performance. Simulation results verify that the sleeping threshold has an optimized value.