Energy Efficiency Maximization with Per-Antenna Power Constraints for Heterogeneous Networks

This paper considers energy efficiency (EE) optimization in downlink multiple-input multiple-output (MIMO) heterogeneous networks (HetNets) in which one macro base station (MBS) and multiple small cell base stations (SBSs) communicate with multiple MIMO users. The primary objective is to design the precoders to maximize the network EE under the constraints on per-antenna and per-base-station transmit power and acceptable interference levels at each user in the macro cell. The design problem results in nonconvex fractional program whose optimal solutions cannot be found directly. In this paper, the relationship between the achievable data rates and the minimum mean square error (MMSE) is adopted to reformulate the design problem into amenable one. Then, an iterative algorithm based the Dinklebach and the block coordinate ascent (BCA) methods is employed for finding optimal precoders. We conduct the numerical simulations to examine the achievable EE performance of the considered HetNets.

I. Introduction

In wireless networks, there have been growing concerns towards improving spectral efficiency (SE) as the number of wireless devices and applications requiring high-speed data transmission has been exponentially increasing. It is predicted that there will be about 12.3 billion mobile devices and global data traffic will reach 77.5 exabytes per month in 2022 [1]. The authors in [2] demonstrated that deploying small cells with high frequency reuse is an effective approach to serve a large number of wireless devices and to increase SE. Small cells with low transmit power can provide transmission links with high quality of service. However, the great number of base stations (BSs) operating in the same frequency would result in significant interference, which may degrade the system performance if interference is not appropriately managed. The research on how to efficiently handle interference and optimize SE in heterogeneous networks (HetNets) has been extensively investigated in the literature [3], [4]. In [3], power control and beamforming methods were studied to minimize interference and maximize the SE in femto cells. The authors of [4] introduced the optimal design for linear transceivers which maximize SE of multiple-input multiple-output (MIMO) broadcasting channels.