Energy-Efficient Multi-Stream Carrier Aggregation for Heterogeneous Networks in 5G Cellular Systems

Multi-stream carrier aggregation (MSCA) has been recently proposed as a mechanism to increase the amount of bandwidth available to users for heterogeneous networks (HetNets) in 5G cellular systems. Previous studies have focused only on maximizing the network capacity and fairness, without considering the energy efficiency of the MSCA. In this paper, the use of MSCA to minimize the energy consumption in a multilayer HetNet is studied. The convexity of the energy minimization problem is examined, leading to the need of a quasiconvex relaxation. With this approximation, an algorithm (BIMEM) is designed to solve the energy minimization problem and obtain an optimum cell-association policy. Since the operators are generally interested in a balance between the energy minimization and capacity maximization, such multi-objective optimization is needed, and we studied it in this paper. The two aforementioned conflicting objectives can be jointly analyzed and solved through scalarization, even though the energy minimization has a quasiconvex objective function, and not a convex one. Performance evaluation is provided to identify the achievable energy savings of our proposed algorithm and to characterize the trade-offs between the energy minimization and capacity maximization in a multi-layer HetNet in 5G systems that support MSCA.