Max-Min Power Optimization in Multigroup Multicast Cell-Free Massive MIMO

In this paper, a multigroup multicast cell-free massive MIMO (CF-mMIMO) system with conjugate beamforming (CB) precoding is considered. In this system, M N-an-tennas access points (APs) distribute in the serving area and coherently serve J×K single-antenna users. All users are randomly divided into J multicast groups. A novel closed-form downlink rate's expression for any M, N, J, and K is derived, which motivates us to propose a weighted max-min power optimization algorithm. In designing this algorithm, the high rate requirements of the high priority groups and the egalitarianism principle are considered. Numerical results demonstrate that the performance improvement achieved by increasing N is visibly better than increasing M. Furthermore, the proposed weighted maxmin fairness algorithm performs well in many respects.