Joint Unicast and Multi-Group Multicast Transmission in Massive MIMO Systems

Abstract

We study the joint unicast and multi-group multicast transmission in massive\nmultiple-input-multiple-output (MIMO) systems. We consider a system model that\naccounts for channel estimation and pilot contamination, and derive achievable\nspectral efficiencies (SEs) for unicast and multicast user terminals (UTs),\nunder maximum ratio transmission and zero-forcing precoding. For unicast\ntransmission, our objective is to maximize the weighted sum SE of the unicast\nUTs, and for the multicast transmission, our objective is to maximize the\nminimum SE of the multicast UTs. These two objectives are coupled in a\nconflicting manner, due to their shared power resource. Therefore, we formulate\na multiobjective optimization problem (MOOP) for the two conflicting\nobjectives. We derive the Pareto boundary of the MOOP analytically. As each\nPareto optimal point describes a particular efficient trade-off between the two\nobjectives of the system, we determine the values of the system parameters\n(uplink training powers, downlink transmission powers, etc.) to achieve any\ndesired Pareto optimal point. Moreover, we prove that the Pareto region is\nconvex, hence the system should serve the unicast and multicast UTs at the same\ntime-frequency resource. Finally, we validate our results using numerical\nsimulations.\n