  In order to cope with the forecasted 1000x increase in wireless capacity
demands by 2030, network operators will aggressively densify their network
infrastructure to reuse the spectrum as much as possible. However, it is
important to realise that these new ultra-dense small cell networks are
fundamentally different from the traditional macrocell or sparse small cell
networks, and thus ultra-dense networks (UDNs) cannot be deployed and operated
in the same way as in the last 25 years. In this paper, we systematically
investigate and visualise the performance impacts of several fundamental
characteristics of UDNs, that mobile operators and vendors should consider when
deploying UDNs. Moreover, we also provide new deployment and management
guidelines to address the main challenges brought by UDNs in the future.
