Downlink SE Analysis and Optimization for Cell-free Massive MIMO Network With Limited-Capacity Fronthauls

This paper derives an asymptotic expression of downlink spectral efficiency (SE) for fronthaul-constrained cell-free massive multiple-input multiple-output (MIMO) network with minimum mean-square error (MMSE) precoding. Based on the closed-form downlink SE, we then formulate an optimization problem to maximize downlink sum SE under the constraints of fronthaul capacity and transmit power. By exploiting the Lagrangian dual transform and fractional programming (FP) techniques, we further propose an alternating maximization (AM) algorithm to achieve bit allocation scheme among all access points (APs) and downlink power control strategy for all users. Finally, simulation results validate the accuracy of the analytical SE and demonstrate that the proposed algorithm is preferable to other counterparts.