  The astounding capacity requirements of 5G have motivated researchers to
investigate the feasibility of many potential technologies, such as massive
multiple-input multiple-output, millimeter wave, full-duplex, non-orthogonal
multiple access, carrier aggregation, cognitive radio, and network
ultra-densification. The benefits and challenges of these technologies have
been thoroughly studied either individually or in a combination of two or
three. It is not clear, however, whether all potential technologies operating
together lead to fulfilling the requirements posed by 5G. This paper explores
the potential benefits and challenges when all technologies coexist in an
ultra-dense cellular environment. The sum rate of the network is investigated
with respect to the increase in the number of small-cells and results show the
capacity gains achieved by the coexistence.
