  Mobile users in an ultra-dense millimeter-wave cellular network experience
handover events more frequently than in conventional networks, which results in
increased service interruption time and performance degradation due to
blockages. Multi-connectivity has been proposed to resolve this, and it also
extends the coverage of millimeter-wave communications. In this paper, we
propose a dual-connection based handover scheme for mobile UEs in an
environment where they are connected simultaneously with two millimeter-wave
cells to overcome frequent handover problems. This scheme allows a mobile UE to
choose its serving link between the two mmWave connections according to the
measured SINRs and then the corresponding base stations may forward duplicate
packets to the UE. We compare our dual-connection based scheme with a
conventional single-connection based scheme through ns-3 simulation. The
simulation results show that the proposed scheme significantly reduces handover
rate and delay. Therefore, we argue that the dual-connection based scheme helps
mobile users achieve performance goals they require in ultra-dense cellular
environments.
