Finally, self-healing covers the tasks related to failure
management and prevention.
This work is focused on the self-healing functionalities
for ultra-dense small cell networks. Self-healing is key
for network OAM automation and performance, since
network failures can lead to service degradations that
might highly impact the brand image and the long-term
revenue of operators. Failure management is divided in
four main subtasks [5]. Firstly, detection consists in the
discovery of network problems, i.e., identifying cells with
degradations in the provided service. Secondly, diagnosis,
also called root cause analysis, aims at identifying
the specific cause or fault producing the degradation.
Finally, once a problem has been detected, different
actions can take place to compensate its effects until recovery
actions restore the network to its full functionality.
In classic failure management approaches, these are
very time consuming and signaling generating tasks.
This makes the automation of these functions a field
attracting an increasing attention, where the implications
of its application for 5G scenarios have been only
scarcely considered.
Moreover, one of the most common problems in small
cell scenarios is the sleeping cell issue, which is the situation
where a base station is not able to properly serve
users, and this is not directly reflected in the OAM
monitoring indicators [6]. The causes behind this problem
range from BS unplugging, failures in the cell hardware,
or incorrect configuration. Since many of these
fault causes behind the sleeping cell issue could be
quickly compensated and/or recovered with automatic
actions (like restarting the BS or updating its software),
fast mechanisms for failure detection/diagnosis are essential
to automatically trigger those tasks. Therefore, detection
and diagnosis should, ideally, identify the failure and
its causes in the range of minutes/seconds.
However, small cells can be particularly prone to failures
(due to its more accessible hardware, use of non-dedicated
backhaul, etc.) and have limited reporting capabilities and
reduced coverage areas which very variable level of use.
Therefore, it is common that not alarm or clear performance
degradation might be reported to the OAM system in
these situations.
Instead, user equipment (UE) positioning information
can serve as an additional input for troubleshooting
of these issues. For example, the knowledge on
UEs location is becoming growlingly available in both
outdoor and indoor scenarios [7]. Localization mechanisms
based on the small cell deployments [8] open
the door to using location to support the OAM tasks.
Even if its use for self-healing in indoor scenarios has
been just recently proposed [9], its usefulness has been
previously demonstrated for macrocell scenarios and other
OAM tasks (e.g., for coverage optimization [10]).
Also, another important limitation of classical approaches
is the high signaling costs of transmitting the monitoring
data to the centralized OAM/SON systems, which might
overload the operator’s network. Additionally, 5G services
and the operation of dense small cell deployments will also
impose very demanding response time and computational
requirements when performed in a centralized manner. In
order to avoid these problems, SON mechanisms should be
as automatic and distributed as possible, avoiding the saturation
of the network and the centralized OAM elements.
Taking all this into account, the present work defines a
novel fully distributed and automated location-based
mechanism for sleeping cell detection and cause diagnosis
in ultra-dense scenarios based on the deployment of
small cells. Here, the required UE locations are assumed
to be provided by external localization sources. The details
of the particular method used for UE localization
are considered outside the scope of the detection/diagnosis
algorithm, making it agnostic to the use of any
localization source. Hence, this paper is organized as follows:
Section 2 discusses the challenges and state of the
art in location-based mechanisms and detection and
diagnosis of sleeping cell issues for the considered small
cells scenario. Section 3 summarizes the characteristics
and assumptions for location-based processing of monitoring
information. The proposed mechanisms for detection
and cause analysis are detailed in sections 4 and 5,
respectively. The combined distributed scheme is then
described in Section 6. The defined system is evaluated
in Section 6 and the conclusions of this study are finally
presented in Section 7.