D2D-Aided Multi-Antenna Multicasting under Generalized CSIT

Multicasting, where a base station (BS) wishes to convey the same message to several user equipments

(UEs), represents a common yet highly challenging wireless scenario. In fact, guaranteeing

decodability by the whole UE population proves to be a major performance bottleneck since the UEs

in poor channel conditions ultimately determine the achievable rate. To overcome this issue, two-phase

cooperative multicasting schemes, which use conventional multicasting in a first phase and leverage

device-to-device (D2D) communications in a second phase to effectively spread the message, have been

extensively studied. However, most works are limited either to the simple case of single-antenna BS or

to a specific channel state information at the transmitter (CSIT) setup. This paper proposes a general

two-phase framework that is applicable to the cases of perfect, statistical, and topological CSIT in the

presence of multiple antennas at the BS. The proposed method exploits the precoding capabilities at the

BS, which enable targeting specific UEs that can effectively serve as D2D relays towards the remaining

UEs, and maximize the multicast rate under some outage constraint. Numerical results show that our

schemes bring substantial gains over traditional single-phase multicasting and overcome the worst-UE

bottleneck behavior in all the considered CSIT configurations.