  With the explosive growth of mobile traffic demand, densely deployed small
cells underlying macrocells have great potential for 5G and beyond wireless
networks. In this paper, we consider the problem of supporting traffic flows
with diverse QoS requirements by exploiting three high frequency bands, i.e.,
the 28GHz band, the E-band, and the Terahertz (THz) band. The cooperation of
the three bands is helpful for maximizing the number of flows with their QoS
requirements satisfied. To solve the formulated nonlinear integer programming
problem, we propose a triple-band scheduling scheme which can select the
optimum scheduling band for each flow among three different frequency bands.
The proposed scheme also efficiently utilizes the resource to schedule flow
transmissions in time slots. Extensive simulations demonstrate the superior
performance of the proposed scheme over three baseline schemes with respect to
the number of completed flows and the system throughput.
