In this paper, we investigate the joint impact of both the number of small BSs and the transmit powers on the energy efficiency (EE) of Heterogeneous cellular networks (HetNets). Based on a typical HetNet structure, we propose a feasible focusing searching algorithm to find the optimal number of small BSs and the corresponding transmit power under coverage and spectral efficiency constraints that maximize the network EE. Simulation results show that there exists an optimal number of small BSs and the transmit power which can not only maximize network EE but also satisfy the constraints.
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