Estimação de qualidade de enlace e alocação dinâmica de canais em redes de sensores sem fio industriais.

Abstract

Industrial Wireless Sensor Networks (IWSNs), that is used to implement monitoring and control applications, presents certain advantages when compared to wired networks, including higher flexibility and lower deployment costs. However, it is necessary to deal with typical problems of wireless networks, such as interference and a high attenuation, in small and large scale. In addition, the characteristics of the wireless channel may change over time, and an IWSN needs to self adapt to these variations to maintain a good quality of service during its operation. Adaptive mechanisms, such as, dynamic channel allocation, are used to deal with the aforementioned problems. For this, the first step is to estimate the link quality, so that the network nodes can decide if a channel change is needed. This thesis presents as a contribution a novel Link Quality Estimator (LQE), and a new type of node, the LQE node, that estimates the quality of the links in real-time, using information obtained from the transceiver, and information obtained from received data packets. The proposed LQE deals with the problems caused by the multipath profile of the environment in channel quality, interference and asymmetry. A prototype was developed and the LQE was validated by experiments in an actual industrial environment. Different from other LQEs in the literature, the solution proposed in this thesis does not cause overhead at the end-nodes and on the network. Based on the proposed LQE, a novel MAC protocol was developed. The protocol uses channel adaptation for the transmission of unicast data packets, and frequency hopping for the transmission of broadcast packets. The packet reception rate at the application layer was at the peak for all scenarios that were evaluated using the proposed protocol, even considering the variations in channel quality over time. The results indicate that the proposed protocol presents a better performance in comparison to the MAC protocols defined by the standards for IWSN, in terms of reliability and determinism. Several experimental results obtained in industrial environments are also described, and a new model for simulation of multi-channel protocols is proposed. The model includes the effects of multipath fading, shadowing, asymmetry, the non-stationary characteristics of the channel, and the uncorrelation of the different channels.