Weighted MMSE Optimization of Conjugate Beamforming for Cell-Free Massive MIMO

Cell-free massive multiple-input multiple-output (MIMO) systems are envisioned to achieve the improved spectral efficiency by supporting users via nearby access points (APs). This work addresses the optimization of beamforming weights for cell-free massive MIMO systems. The connectivity level constraints are taken into account to accommodate finite-rate fronthaul links. The minimum rate maximization problem is tackled by the weighted minimum mean squared error (WMMSE) algorithm. Numerical results show that the proposed scheme achieves significantly improved performance than a baseline scheme in overall signal-to-noise ratio (SNR) regime.