  Millimeter-wave has become an integral part of 5G networks to meet the
ever-increasing demand for user data throughput. Employing higher carrier
frequencies introduces new challenges for the propagation channel such as
higher path loss and rapid signal degradations. On the other hand, higher
frequencies allow deployment of small-sized antenna elements that enable
beamforming. To investigate user mobility under these new propagation
conditions, a proper model is needed that captures spatial and temporal
characteristics of the channel in beamformed networks. Current channel models
that have been developed for 5G networks are computationally inefficient and
lead to infeasible simulation time for most user mobility simulations. In this
paper, we present a simplified channel model that captures the spatial and
temporal characteristics of the 5G propagation channel and runs in feasible
simulation time. To this end, coherence time and path diversity originating
from fully fledged Geometry based Stochastic Channel Model (GSCM) are analyzed
and adopted in Jakes channel model. Furthermore, the deviation of multipath
beamforming gain from single ray beamforming gain is analyzed and a regression
curve is obtained to be used in the system-level simulations. We show through
simulations that the proposed simplified channel model leads to mobility
results comparable to Jakes model for high path diversity. Moreover, the
multi-path beamforming gain increases the interference in the system and in
turn number of mobility failures.
