  We study downlink beamforming in a single-cell network with a multi-antenna
base station (BS) serving cache-enabled users. For a given common rate of the
files in the system, we first formulate the minimum transmit power with
beamforming at the BS as a non-convex optimization problem. This corresponds to
a multiple multicast problem, to which a stationary solution can be efficiently
obtained through successive convex approximation (SCA). It is observed that the
complexity of the problem grows exponentially with the number of subfiles
delivered to each user in each time slot, which itself grows exponentially with
the number of users in the system. Therefore, we introduce a low-complexity
alternative through time-sharing that limits the number of subfiles that can be
received by a user in each time slot. It is shown through numerical simulations
that, the reduced-complexity beamforming scheme has minimal performance gap
compared to transmitting all the subfiles jointly, and outperforms the
state-of-the-art low-complexity scheme at all SNR and rate values with
sufficient spatial degrees of freedom, and in the high SNR/high rate regime
when the number of spatial degrees of freedom is limited.
