  Previous works on cache-enabled small-cell networks (SCNs) with probabilistic
caching often assume that each user is connected to the nearest small base
station (SBS) among all that have cached its desired content. The user may,
however, suffer strong interference from other SBSs which do not cache the
desired content but are geographically closer. In this work, we investigate
this issue by deploying multiple antennas at each SBS. We first propose a
user-centric SBS clustering model where each user chooses its serving SBS only
from a cluster of $K$ nearest SBSs with $K$ being a fixed cluster size. Two
beamforming schemes are considered. One is coordinated beamforming, where each
SBS uses zero-forcing (ZF) beamformer to null out the interference within the
coordination cluster. The other is uncoordinated beamforming, where each SBS
simply applies matched-filter (MF) beamformer. Using tools from stochastic
geometry, we obtain tractable expressions for the successful transmission
probability (STP) of a typical user for both cases in the high signal-to-noise
ratio (SNR) region. Tight approximations in closed-form expressions are also
obtained. We then formulate and solve the optimal probabilistic caching problem
to maximize the STP. Numerical results reveal interesting insights on the
choices of ZF and MF beamforming in multi-antenna cache-enabled SCNs.
