Kallol Das

Wireless Industrial Monitoring and Control Networks: The Journey So Far and the Road Ahead

While traditional wired communication technologies have played a crucial role in industrial monitoring and control networks over the past few decades, they are increasingly proving to be inadequate to meet the highly dynamic and stringent demands of today’s industrial applications, primarily due to the very rigid nature of wired infrastructures. Wireless technology, however, through its increased pervasiveness, has the potential to revolutionize the industry, not only by mitigating the problems faced by wired solutions, but also by introducing a completely new class of applications. While present day wireless technologies made some preliminary inroads in the monitoring domain, they still have severe limitations especially when real-time, reliable distributed control operations are concerned. This article provides the reader with an overview of existing wireless technologies commonly used in the monitoring and control industry. It highlights the pros and cons of each technology and assesses the degree to which each technology is able to meet the stringent demands of industrial monitoring and control networks. Additionally, it summarizes mechanisms proposed by academia, especially serving critical applications by addressing the real-time and reliability requirements of industrial process automation. The article also describes certain key research problems from the physical layer communication for sensor networks and the wireless networking perspective that have yet to be addressed to allow the successful use of wireless technologies in industrial monitoring and control networks.

Censoring for Bayesian Cooperative Positioning in Dense Wireless Networks

Cooperative positioning is a promising solution for location-enabled technologies in GPS-challenged environments. However, it suffers from high computational complexity and increased network traffic, compared to traditional positioning approaches. The computational complexity is related to the number of links considered during information fusion. The network traffic is dependent on how often devices share positional information with neighbors. For practical implementation of cooperative positioning, a low-complexity algorithm with reduced packet broadcasts is thus necessary. Our work is built on the insight that for precise positioning, not all the incoming information from neighboring devices is required, or even useful. We show that blocking selected broadcasts (transmit censoring) and discarding selected incoming information (receive censoring) based on a Cramer-Rao bound criterion, leads to an algorithm with reduced complexity and traffic, without significantly affecting accuracy and latency.

Censored cooperative positioning for dense wireless networks

Cooperative positioning is an emerging topic in wireless sensor networks and navigation. It can improve the positioning accuracy and coverage in GPS-challenged conditions such as inside tunnels, in urban canyons, and indoors. Different algorithms have been proposed relying on iteratively exchanging and updating positional information. For the purpose of computational complexity, network traffic, and latency, it is desirable to minimize the amount of information shared between devices, while still maintaining acceptable performance. We show that information that is not reliable should not be shared, and information that is not informative should not be used. This naturally leads to censoring schemes. We consider different censoring schemes based on the Cramér Rao bound (CRB). We find that by blocking the broadcasts of the nodes that do not have reliable estimates (transmit censoring) and selecting the most usable links after receiving signals from neighbors (receive censoring), complexity and traffic can be reduced significantly without degrading positioning performance.

Evaluation of DECT-ULE for robust communication in dense wireless sensor networks

In todays world wireless sensor networks (WSNs) have enormous applications which made our everyday life much easier. In most of these applications, the unlicensed 2.4 GHz frequency band has been used for sensor communications. Due to the wide use, the chance of getting interference in this frequency band is quite high. Thus, a reliable and real-time communication in mass WSNs can not be guaranteed, which is essential for industrial applications. In this paper, we evaluate the performance of Digital Enhanced Cordless Telecommunications - Ultra Low Energy (DECT-ULE) for robust communication in dense WSNs and found that it can cope with the limitations of existing standards. We show that DECT-ULE can elegantly handle dense WSNs by allocating communication channels with excellent quality and minimum delay.

Wireless sensor network for helicopter rotor blade vibration monitoring: Requirements definition and technological aspects

The main rotor accounts for the largest vibration source for helicopter fuselage and components. However, accurate blade monitoring has been limited due to the practical restrictions on instrumenting rotating blades. The use of Wireless Sensor Networks (WSNs) for real time vibration monitoring promises to deliver a significant contribution to rotor performance monitoring and blade damage identification. This paper discusses the main technological challenges for wireless sensor networks for vibration monitoring on helicopter rotor blades. The first part introduces the context of vibration monitoring on helicopters. Secondly, an overview of the main failure modes for rotor and blades is presented. Based on the requirements for failure modes monitoring, a proposition for a multipurpose sensor network is presented. The network aims to monitor rotor performance, blade integrity and damage monitoring at three different scales referred to as macro layer, meso layer and micro layer. The final part presents the requirements for WSNs design in relation with sensing, processing, communication and actuation. Finally power supply aspects are discussed.

Evaluation of DECT for low latency real-time industrial control networks

Wireless sensor networks (WSNs) have revolutionized the industrial networks by enabling wireless sensing and control to the machine parts where wiring is impossible. However, new challenges in terms of communication reliability and latency, appear with the advances in the industrial wireless control systems. Existing standards are found inadequate to support many of these demanding situations as most of those are based on IEEE 802.15.4 standard, which is unable to provide high communication reliability with low latency (milliseconds). Digital Enhanced Cordless Telecommunications (DECT), a communication standard developed by European Telecommunications Standards Institute (ETSI), seems to support the timing and reliability requirements of modern industrial wireless control networks. In this paper, we evaluate the performance of DECT in various industrial environments and found that it can maintain excellent communication reliability between sensors and control centre with low latency in such scenarios.

A network traffic reduction method for cooperative positioning

Cooperative positioning is suitable for applications where conventional positioning fails due to lack of connectivity with a sufficient number of reference nodes. In a dense network, as the number of cooperating devices increases, the number of packet exchanges also increases proportionally. This causes network congestion and increases packet collisions. In order to maintain the quality of positioning, we need to reduce loss of information due to collisions. This can achieved by reducing the broadcast of unnecessary information. We show that by intelligently suppressing the transmission of selected nodes, the overall network traffic can be reduced without degrading the positioning performance significantly.

Efficient I/O joining and reliable data publication in energy harvested ISA100.11a network

Energy harvesting technologies have brought a paradigm shift in the industrial automation sector by procreating self-powered wireless input/output (I/O) devices. Unfortunately, current wireless technologies for industrial applications, such as ISA100.11a and WirelessHART, are yet far from supporting harvester powered I/O devices. Although several works have been conducted to address the requirements of energy harvested I/O devices, most of those have focused on minimizing the I/O energy consumption during the steady-state phase of the network. However, a very important aspect, the energy consumption during network joining that consumes a significant amount of energy, is overlooked in these works. In this paper, we therefore analyze the I/O energy consumption in ISA100.11a network during the joining phase in addition to that in normal operation to better understand the challenges of energy harvesting communications. Then, we propose an energy efficient network joining scheme to support harvester powered I/O devices in ISA100.11a network. The proposed scheme significantly reduces the joining delay when compared with the traditional ISA100.11a joining scheme. We also propose a reliable data transmission scheme for energy harvested I/O devices by utilizing spatial diversity that can outperform ISA100.11a data publication through significant improvement in packet reception.

D-MHR: A distributed management scheme for hybrid networks to provide real-time industrial wireless automation

Current wireless technologies for industrial application, such as WirelessHART and ISA100.11a, use a centralized management approach which makes it difficult and costly for harvester-powered I/O devices to re-join the network in case of power failure. The communication overhead and delay to cope with the dynamic environment of a large-scale industrial network are also very high for an I/O device. In this paper, we therefore propose a distributed management scheme named D-MHR, which can address the requirements of energy constrained I/O devices. In D-MHR, the routers can dynamically reserve communication resources and manage the I/O devices in the local star sub-networks. We demonstrate that D-MHR achieves higher network management efficiency compared to IS100.11a standard, without compromising the latency and reliability requirements of industrial wireless networks.

A distributed management scheme for supporting energy-harvested I/O devices

Current wireless technologies for industrial application, such as WirelessHART and ISA100.11a, are not designed to support harvester-powered input/output (I/O) devices, where energy availability varies in a non-deterministic manner. The centralized management approach of these standards makes it difficult and costly for harvester-powered I/O devices (sensor/actuators) to re-join in the network in case of power failure. The communication overhead and delay to cope with the dynamic environment of a large-scale industrial network are also very high for an I/O device. In this paper, we therefore propose a Distributed Management scheme for Hybrid networks to provide Real-time communication (D-MHR) based on the IEEE 802.15.4e and Routing Protocol for Low power and Lossy Networks (RPL) standards, which can address the requirements of energy constrained I/O devices. In D-MHR, the routers can dynamically reserve communication resources and manage the I/O devices in the local star sub-networks. We demonstrate that D-MHR achieves higher network management efficiency compared to IS100.11a standard, without compromising the latency and reliability requirements of industrial wireless networks.