On the Performance of Multigroup Multicast Cell-Free Massive MIMO

We investigate the performance of a multigroup multicast cell-free massive multiple-input multiple-output system where many access points (APs) multicast signals to many groups of users. A distributed conjugate beamforming with short-term power constraint (STPC) policy is proposed to use at the APs. In addition, we propose a new transmission scheme in which the APs beamform pilots so that each user can estimate the effective channel gains for signal detection. The analytical expressions for the per-user net throughputs are derived. The results show that when the number of groups is small, STPC outperforms long-term power constraint used in the literature. Furthermore, at a small number of user groups, the transmission with downlink pilots improves the system performance noticeably.