Energy-Efficiency-Oriented Joint User Association and Power Allocation in Distributed Massive MIMO Systems

This paper investigates the energy efficient downlink transmission in distributed massive multiple-input-multiple-output systems, where massive antennas are clustered on geographically distributed remote radio heads (RRH). A closed form of the ergodic achievable rate is derived for a specific RRH-user association and imperfect channel state information to assist the formulation of its system energy efficiency (EE). By assuming minimum user achievable rate requirements and a practical power consumption model including both the transmit power and the antenna circuit power, an optimization problem is formulated to maximize the system EE with respect to the power allocation, the antennas activation, and the RRH-user association in a combinatorial manner. The formulated problem is a mixed-integer nonlinear programming problem, which is NP-hard and usually has no feasible solution. To solve it, an efficient algorithm is proposed by utilizing hierarchical decomposition technique and iterative successive convex approximation. The feasibility as well as the effectiveness of the proposed algorithm are analyzed and proved through analysis and intensive computer simulations. Results show that the system EE can be greatly improved by the proposed scheme.