  With over-deployed network infrastructures, network densification is shown to
hinder the improvement of user experience and system performance. In this
paper, we adopt multi-antenna techniques to overcome the bottleneck and
investigate the performance of single-user beamforming, an effective method to
enhance desired signal power, in small cell networks from the perspective of
user coverage probability (CP) and network spatial throughput (ST).
Pessimistically, it is proved that, even when multi-antenna techniques are
applied, both CP and ST would be degraded and even asymptotically diminish to
zero with the increasing base station (BS) density. Moreover, the results also
reveal that the increase of ST is at the expense of the degradation of CP.
Therefore, to balance the tradeoff between user and system performance, we
further study the critical density, under which ST could be maximized under the
CP constraint. Accordingly, the impact of key system parameters on critical
density is quantified via the derived closed-form expression. Especially, the
critical density is shown to be inversely proportional to the square of antenna
height difference between BSs and users. Meanwhile, single-user beamforming,
albeit incapable of improving CP and ST scaling laws, is shown to significantly
increase the critical density, compared to the single-antenna regime.
