Joint user association and power allocation for massive MIMO HetNets with imperfect CSI

Since Massive multiple-input and multiple-output (MIMO) and heterogeneous networks (HetNets) have significantly improvement in spectrum efficiency, Massive MIMO enabled HetNets have emerged as a promising technique for the fifth-generation cellular networks. Most previous studies focus on energy-efficient resource allocation of Massive MIMO HetNets by assuming perfect channel state information (CSI). In this paper, we investigate the alpha-fairness network utility optimization problem of joint user association and power allocation for a downlink Massive MIMO HetNet with imperfect CSI. By utilizing zero-forcing beamforming, we show a new closed-form lower bound expression on the ergodic achievable rate. Furthermore, we formulate the optimization problem as a mixed-integer nonlinear programming problem, which is non-convex and NP-hard, to achieve the maximization of alpha-fairness network utility. Consequently, a joint iterative algorithm with respect to user association and power allocation is developed by decomposing the original problem and relaxing the constraints. Simulation results show that our proposed algorithm can yield much better network utility performance than the other algorithms. (C) 2020 Elsevier B.V. All rights reserved.