Sum-rate maximization in the simultaneous unicast and multicast services with two users

Recently, there has been great interest in the multicast service where a common content such as video streaming and TV program is intended for multiple users. However, while receiving the common message, the users may also wish to receive their personal messages. Therefore, in this paper, we consider a multiple-antenna base station communicating with two single-antenna users and there are a common message to be received by both as well as private messages for each user. Then, we propose to transmit the superposition of the common stream and the private stream intended to only the user with the largest channel gain where each stream is beamformed. An algorithm to determine the optimal beamforming vectors such that the system sum rate is maximized subject to power constraint is presented. Furthermore, the associated achievable rate region is also employed to gain more insight into the achievable sum rate. Our simulation results show that the proposed scheme achieves higher sum rate compared to the conventional schemes especially in the unequal channel gain case.