Industrial Wireless Sensor Networks - Simulation and measurement in an interfering environment

Recently the research community is considering with a growing interest the adoption of IWSN in application contexts such as real-time (industrial) communications and distributed measurement systems. These types of applications typically impose very tight requirements to the underlying communication systems and, moreover, they might have to cope with the intrinsic unreliability of wireless networks. It is hence needed an accurate characterization of these networks' behavior, from a metrological point of view. Suitable measurement systems have to be realized, and experiments performed aimed at evaluating some of the most appropriate performance indicators. Unfortunately, despite the appealing opportunities provided by IWSN, their adoption is just at its beginning. It is clear that a comprehensive experimental analysis of their behavior would improve theoretical analysis, simulations and design of the network, since the consequent increased accuracy of models could reduce the source of difference between real and expected behaviors. With the work presented in this thesis the author would provide some original contribution in the field of measurements on real-time wireless networks adopted for industrial communications and distributed measurement systems. In this context, one of the most relevant aspect to be considered is represented, as described in the literature, by interference that possibly arises from "intentional" communications taking place in external systems. In order to address such an issue, some simulation techniques have been considered. As a result, they lead to the development of a network simulator software tool that enabled a cross-layer analysis of interference. This activity stimulated an in-depth study of the IEEE802.15.4 and IEEE802.11 communication protocols. Particularly, medium access techniques have been analyzed in the perspective of IWSN applications. On this basis new and effective methods for increasing the network reliability have been proposed, along with fair packet retransmission scheduling methods. Moreover, new rate adaptation algorithms for wireless networks specifically designed for real-time communication purposes, exploiting the high robustness of low transmission rates have been proposed. Finally, since the reliability of a network strongly depends on the real behavior of the employed devices, an experimental approach for the measurement of the devices characteristics is presented, with the aim of providing suitable models and methods for designers.