  Deploying sub-6GHz network together with millimeter wave (mmWave) is a
promising solution to simultaneously achieve sufficient coverage and high data
rate. In the heterogeneous networks (HetNets), the traditional coupled access,
i.e., the users are constrained to be associated with the same base station in
both downlink and uplink, is no longer optimal, and the concept of downlink and
uplink decoupling has recently been proposed. In this paper, we propose an
analytical framework to investigate the traditional sub-6GHz HetNets
integrating with mmWave small cells (SCells) with decoupled access, where both
the uplink power control and mmWave interference are taken into account. Using
the tools from stochastic geometry, the performance metrics of
signal-to-interference-plus-noise ratio coverage probability, user-perceived
rate coverage probability, and area sum rate are derived. The impact of the
densification of different SCells on the network performance is also analyzed
to give insights on the network design. Simulation results validate the
accuracy of our analysis, and reveal that mmWave interference can not be
neglected when the mmWave SCells are extremely dense and that different kinds
of SCells have various effects on the network performance and thus need to be
organized properly.
