QUEIROS, D. V.; http://lattes.cnpq.br/3282540449376241; QUEIROZ, Diego Véras de.
Resumo:
Recent advances in wireless sensor networks (WSN), especially in industrial environments
(IWSN), have brought important improvements for the deployment of a sensor network
in such environments. However, there is a high level of interference, noise, shadowing,
and multipath fading in industry, caused by machinery, metallic objects and obstructions,
which can affect the quality of the link. Some mechanisms have been proposed to mitigate
the negative effects, such as frequency hopping and channel blacklisting. However, there
are still open issues, such as an appropriate method of managing both mechanisms
to avoid similar or adjacent channels in simultaneous transmissions. The use of a link
quality estimator (LQE), with adequate channel assignment, helps to increase network
performance. In addition to the use of estimators, this thesis proposes two approaches
that separate the channels according to the temporary profile of each one and insert
them into lists. The aim is to better deal with the negative effects of the environment
on the transmission medium. The first uses a double channel list (alowlist and denylist),
and the second uses a triple list of channels (denylist, greylist, and alowlist). In both,
the management of channel offset was considered to avoid collisions and reduce internal
interference in simultaneous transmissions. The denylist has low quality channels, the
greylist has channels with uncertain quality, and the alowlist has good quality channels.
A fuzzy logic method was used in the triple list approach to classify the channels in the
most appropriate list. The two proposals were compared by means of simulation using the
frequency hopping method based on the TSCH protocol of the IEEE 802.15.4e standard
for WSN. In the study, networks in star and tree topologies were analyzed, with and
without link quality estimators, with and without collisions, using a realistic channel
model for IWSN. The results of the experiments showed that in the tree topology the
approaches with double and triple list presented better performances than the approach
without link quality estimators, in terms of package delivery rate and determinism, and
that the triple list surpassed the double list in more dynamic networks. In star topology,
the larger the size of the denylist, the better the network performance, as the devices use
only the best channels.