Ivanovitch M. D. Silva

Reliability and Availability Evaluation of Wireless Sensor Networks for Industrial Applications

Wireless Sensor Networks (WSN) currently represent the best candidate to be adopted as the communication solution for the last mile connection in process control and monitoring applications in industrial environments. Most of these applications have stringent dependability (reliability and availability) requirements, as a system failure may result in economic losses, put people in danger or lead to environmental damages. Among the different type of faults that can lead to a system failure, permanent faults on network devices have a major impact. They can hamper communications over long periods of time and consequently disturb, or even disable, control algorithms. The lack of a structured approach enabling the evaluation of permanent faults, prevents system designers to optimize decisions that minimize these occurrences. In this work we propose a methodology based on an automatic generation of a fault tree to evaluate the reliability and availability of Wireless Sensor Networks, when permanent faults occur on network devices. The proposal supports any topology, different levels of redundancy, network reconfigurations, criticality of devices and arbitrary failure conditions. The proposed methodology is particularly suitable for the design and validation of Wireless Sensor Networks when trying to optimize its reliability and availability requirements.

A dependability evaluation tool for the Internet of Things

The Internet of Things (IoT) is a promising networking paradigm which immerses objects (cell phones, goods, watches, sensing motes, TVs, etc.) in a worldwide connection. Despite its high degree of applicability, the IoT faces some challenges. One of the most challenging problems is its dependability (reliability and availability), since a device failure might put people in danger or result in financial loss. The lack of a design tool for assessing the dependability of IoT applications at the early planning and design phases prevents system designers from optimizing their decisions so as to minimize the effects of such faults on the network devices. In this paper, we propose a dependability evaluation tool for IoT applications, when hardware faults and permanent link faults are considered.

Routing and Scheduling Algorithms for WirelessHARTNetworks: A Survey

Wireless communication is a trend nowadays for the industrial environment. A number of different technologies have emerged as solutions satisfying strict industrial requirements (e.g., WirelessHART, ISA100.11a, WIA-PA). As the industrial environment presents a vast range of applications, adopting an adequate solution for each case is vital to obtain good performance of the system. In this context, the routing and scheduling schemes associated with these technologies have a direct impact on important features, like latency and energy consumption. This situation has led to the development of a vast number of routing and scheduling schemes. In the present paper, we focus on the WirelessHART technology, emphasizing its most important routing and scheduling aspects in order to guide both end users and the developers of new algorithms. Furthermore, we provide a detailed literature review of the newest routing and scheduling techniques for WirelessHART, discussing each of their features. These routing algorithms have been evaluated in terms of their objectives, metrics, the usage of the WirelessHART structures and validation method. In addition, the scheduling algorithms were also evaluated by metrics, validation, objectives and, in addition, by multiple superframe support, as well as by the redundancy method used. Moreover, this paper briefly presents some insights into the main WirelessHART simulation modules available, in order to provide viable test platforms for the routing and scheduling algorithms. Finally, some open issues in WirelessHART routing and scheduling algorithms are discussed.

A dependability evaluation for Internet of Things incorporating redundancy aspects

The Internet of Things (IoT) is a promising networking paradigm which immerses objects (cell phones, goods, watches, sensing motes, TVs, etc.) in a worldwide connection. Despite its high degree of applicability, the IoT faces some challenges. One of the most challenging problems is its dependability (reliability and availability), since a device failure might put people in danger or result in financial loss. An alternative to mitigate these consequences is the adoption of a strategy based on spare devices. If a primary device fails, the spare device could assume its functions in a safe way. Thus, this work proposes mathematical models based on Markov Chain which is able to estimate the reliability and availability of IoT applications considering redundancy aspects. The proposal can be used in order to provide valuable data at the early planning and design phases of an IoT application.

Towards a WirelessHART module for the ns-3 simulator

This work has the objective to present the first development results of a WirelessHART module for the ns-3. Our focus is the implementation of the Physical layer in order to provide the basis for the development of the superior layers such as MAC and Application. Thus, we presente an energy consumption model, a Gilbert/Elliot error model and an analysis for the currently avaliable ns-3 propagation loss models. For further development we mainly aim for the implementation of the time slot scheduler (Network Manager) and the development of an inter protocol simulation with mutual interference.

Performance evaluation of WirelessHART networks using a new network simulator 3 module

Nowadays, wireless communication is a tendency in industrial environments, enabling the addition of new applications and saving resources when compared to their wired counterparts. In this context, the WirelessHART specification is emerging as a solution for the last mile connection. Despite its high degree of applicability, a WirelessHART network faces some challenges. Some of the most challenging problems are its reliability, energy consumption, and interference from the environment, issues which involve the lower layers. In order to enable performance evaluations in a low cost and scalable way, we propose a new NS-3 module for the WirelessHART physical layer including an error model (Gilbert/Elliot), station positioning, signal attenuation and energy consumption. Furthermore, the module permits configuring each link with different fault probabilities, allowing more accurate simulations. For validation, the scheduling and routing approaches were statically configured assuming different topologies and probabilistic error scenarios already validated in the literature.

Selecting redundant nodes when addressing availability in wireless visual sensor networks

As Wireless Sensor Networks have been employed to support critical monitoring applications, network availability has become a major design concern. In these networks, redundancy can be exploited to enhance the attainable availability level, where redundant sensors can replace faulty nodes. When camera-enabled sensors are deployed to retrieve visual information, the perception of redundancy changes considerably, since the redundancy of visual sensors depends on the monitoring requirements of the applications. In such context, characteristics as deployment density, viewing angle and sensing range are relevant when planning wireless sensor network applications, directly impacting in the number of redundant nodes. We propose an algorithm to select redundant nodes in Wireless Visual Sensor Networks, according to the application requirements. Moreover, we discuss how parameters of the deployed network can influence on the number of redundant nodes.

Performance evaluation of a compression algorithm for wireless sensor networks in monitoring applications

Wireless sensor network (WSN) is an emerging technology that targets multiple applications in the different environments. Its infrastructure is composed of a large number of sensor nodes with a limited physical capacity and low cost. The energy consumption must be as optimized as possible in order to extend its lifetime. The use of data compression techniques can be an advantage in the WSN context, once these techniques eliminate transmission of redundant information and consequently can be adopted to minimize the consumption of energy in the sensor nodes. WSN for monitoring applications can benefit from this technique as it may maximize the lifetime of batteries. The main motivation of this paper is to investigate the performance of a data compression algorithm for WSN in the context of monitoring applications. To validate the proposal, simulation experiments have been performed using the Network Simulator (NS-2) tool.

Availability assessment of wireless visual sensor networks for target coverage

Visual monitoring in wireless sensor networks can provide valuable information of the monitored field, enriching surveillance and control applications. For those networks, however, some active visual sources may fail or run out of energy, potentially degrading the application monitoring quality. Visual sensors may be deployed to monitor a set of targets that are critical for the monitoring tasks of the application, demanding some level of redundancy to compensate sensor failures. In this context, it may be desired to know the probability of a specific target to be covered by at least one visual sensor along the network operation. We propose an approach for the availability assessment in wireless visual sensor networks for the specific case of target coverage, relating sensing redundancy to energy discharging and sensors disconnection. The proposed approach can then be used to predict coverage holes, directly benefiting critical monitoring applications.

Assessment of WirelessHART networks in closed-loop control system

Wireless communication is currently the trend in industrial environments, reducing costs and allowing the creation of applications that were impossible with legacy technologies. In this respect, the WirelessHART specification is emerging as a standard solution. Despite the direct benefits, a WirelessHART network exhibits a series of technical (reliability, energy consumption, tolerance to failures, constant delays) and cultural challenges. Accordingly the demand for tools to assess and guarantee reliability in closed-loop control systems becomes imminent. With the aim of demystifying the use of wireless technology in closed-loop control systems in the industry, this paper presents an assessment of the behavior of a WirelessHART network in a water level control processes in a system of coupled tanks. The results indicate that some challenges need to be overcome to adopt wireless technologies in control applications, as the case of transmission rates requirements less than one second.