1 Introduction
Current studies on 5G focus on three main objectives:
converged fiber-wireless, super-efficient, and super-fast
mobile networks [1]. To achieve the last two objectives,
5G networks are expected to hugely increase network
densification. For these, the ultra-dense deployment of
small cells or DenseNets (with a few tens of meters
inter-site distance) will be one of the main approaches
used to reach the upcoming coverage and throughput
requirements [2]. Small cells consist on low-powered,
low-range base stations (BSs) used to cover especially
difficult radio locations, as well as to increase network
capacity for specific hotspots. Small cells are already started
to become a common approach to provide coverage indoors
(e.g., malls or offices) or to shadowed locations. They
are also employed to serve high demanding spots (e.g.,
airports, stadiums, etc.). Different small cell models
have been defined for indoor scenarios, such as picocells,
i.e., cells with up to 200-m coverage, and femtocells, i.e.,
cells with coverage in the range of tens of meters and
making use of broadband non-dedicated infrastructure,
e.g., digital subscriber line (DSL), to connect with the operator’s
network [3].
The large number of small cells, together with the growing
coexistence of multiple radio access technologies
(RATs) like global system for mobile communications
(GSM), universal mobile telecommunications system
(UMTS), long-term evolution (LTE), etc., leads to an
increasing complexity in the operations, administration,
and management (OAM) of cellular networks. In order to
overcome this complexity, the Next Generation Mobile
Networks (NGMN) Alliance and the 3rd Generation
Partnership Project (3GPP) introduced the concept of
self-organizing networks (SON), which aims to automate
the OAM procedures [4], reducing costs and increasing
the network performance and quality of service. SON encompasses
three main categories: self-configuration, which
is related to the capability of automatically deploying new
elements in a network and self-optimization, on the ability
* Correspondence: rbm@ic.uma.es of the network to adapt to changing service requirements.