  We experience a major paradigm change in mobile networks. The infrastructure
of cellular networks becomes mobile as it is densified by using mobile and
nomadic small cells to increase coverage and capacity. Furthermore, the
innovative approaches such as green operation through sleep scheduling,
user-controlled small cells, and end-to-end slicing will make the network
highly dynamic. Mobile cells, while bringing many benefits, introduce many
unconventional challenges that we present in this paper. We have to introduce
novel techniques for adapting network functions, communication protocols and
their parameters to network density. Especially when cells on wheels or wings
are considered, static and man-made configurations will waste valuable
resources such as spectrum or energy if density is not considered as an
optimization parameter. In this paper, we present the existing density
estimators. We analyze the impact of density on coverage, interference,
mobility management, scalability, capacity, caching, routing protocols and
energy consumption. We evaluate nomadic cells in dynamic networks in a
comprehensive way and illustrate the potential objectives we can achieve by
adapting mobile networks to base station density. The main challenges we may
face by employing dynamic networks and how we can tackle these problems are
discussed in detail.
