  The integration of millimeter-wave base stations (mmW-BSs) with conventional
microwave base stations ($\mu$W-BSs) is a promising solution for enhancing the
quality-of-service (QoS) of emerging 5G networks. However, the significant
differences in the signal propagation characteristics over the mmW and $\mu$W
frequency bands will require novel cell association schemes cognizant of both
mmW and $\mu$W systems. In this paper, a novel cell association framework is
proposed that considers both the blockage probability and the achievable rate
to assign user equipments (UEs) to mmW-BSs or $\mu$W-BSs. The problem is
formulated as a one-to-many matching problem with minimum quota constraints for
the BSs that provides an efficient way to balance the load over the mmW and
$\mu$W frequency bands. To solve the problem, a distributed algorithm is
proposed that is guaranteed to yield a Pareto optimal and two-sided stable
solution. Simulation results show that the proposed matching with minimum quota
(MMQ) algorithm outperforms the conventional max-RSSI and max-SINR cell
association schemes. In addition, it is shown that the proposed MMQ algorithm
can effectively balance the number of UEs associated with the $\mu$W-BSs and
mmW-BSs and achieve further gains, in terms of the average sum rate.
