  Next generation (5G) cellular networks are expected to be supported by an
extensive infrastructure with many-fold increase in the number of cells per
unit area compared to today. The total energy consumption of base transceiver
stations (BTSs) is an important issue for both economic and environmental
reasons. In this paper, an optimization-based framework is proposed for
energy-efficient global radio resource management in heterogeneous wireless
networks. Specifically, with stochastic arrivals of known rates intended for
users, the smallest set of BTSs is activated with jointly optimized user
association and spectrum allocation to stabilize the network first and then
minimize the delay. The scheme can be carried out periodically on a relatively
slow timescale to adapt to aggregate traffic variations and average channel
conditions. Numerical results show that the proposed scheme significantly
reduces the energy consumption and increases the quality of service compared to
existing schemes in the literature.
