Industry 4.0 Vision for the Supply of Energy and Materials. Группа авторов

such as virtual reality for remote maintenance worker assistance and production line imaging for quality inspection significantly benefit from the higher bandwidth available through 5G eMBB. In addition to fast data rate, 5G eMBB provides low latency of 4 ms over the air, enabling real-time data transmission, processing, and decision-making for autonomous warehousing robots and industrial machine control [167]. One approach for providing eMBB is to implement millimeter wave (mm-wave) technology and install high-frequency mm-wave antennas [168].

      1.5.4.3 Massive Machine Type Communication

The 5G solution that serves a large number of MTC applications is mMTC, which deals with scalable connectivity for massive number of devices. 5G offers wireless communication to over 1 million IoT terminals (with diverse QoS requirements) per square kilometer of area [169]. mMTC data communication is typically infrequent, making it ideal for alerting systems or periodic sampling (e.g., indicating manufacturing equipment failure and low frequency environmental sensing). This feature is suitable for a wide range of use cases across utilities, industrial campuses, and logistics. mMTC should handle different exceptional challenges, such as varied and intermittent traffic, QoS provisioning, large signaling overhead, and congestion in RAN [137].

      1.6 Wireless System Design Enablers and Metrics for Emerging IIoT Applications

      IIoT is one of the key components of the Fourth Industrial Revolution. It provides customized architectures and standardized interfaces for data acquisition, transmission, and analytics in industrial applications [25]. Diverse industrial applications differ in terms of operational settings, technical requirements, and service environments. Therefore, it is not possible to provide one multi-purpose wireless solution for all IIoT use cases. Each wireless system design requires theoretical and experimental measures based on its expected performance. In this section, we first review conventional technical enablers in design of wireless networks for IIoT and then discuss the metrics on the desired performance.

      1.6.1 General Technical Enablers in Design of Wireless Network for IIoT

      The National Institute of Standards and Technology (NIST) proposed a reference framework as a guideline that helps users select and design a given wireless system, customize its configuration based on the specific application requirements, successfully deploy it, and finally ensure its performance for industrial environments [55]. Based on this framework, the design of industrial wireless communication should be evaluated from three major aspects: system modeling and verification, radio resource management (RRM) schemes, and protocol interfaces design.

      1.6.1.1 System Modeling and Verification

      The connectivity in IIoT systems could exploit well-established communication protocols to reduce network configurations and customizations. However, the increasing integration of communication into automation aspects makes IIoT systems more complex and prone to errors (e.g., device failures, mistakes in configuration). Given that failure in communication may be catastrophic in industrial applications using IIoT, it is essential to use proper system models and verification schemes to increase the level of certainty in IIoT systems. There are different approaches to create system models, such as theoretical inference and simulation tests.

An important reference in IIoT wireless system design is modeling data traffic patterns to capture and predict the dynamic behavior of systems and handle system complexity. However, we initially need to understand the theoretical basis of inference models and the conditions underlying their effectiveness before choosing the method apt to IIoT environments and service characteristics. This justifies a rising need for network simulation platforms and testbeds that emulate real-world industrial systems and perform system-level verification [170]. The simulation frameworks could also assist in performance evaluation of wireless networks for the next-generation factories and process automation systems [171].

      1.6.1.2 Radio Resource Management

The rise of ultra-dense and dynamic wireless networks in the Industry 4.0 paradigm implies a further number of simultaneous transmissions. Therefore, it is necessary to efficiently utilize limited wireless resources such as RF spectrum resources and radio network infrastructure to fulfill strict QoS requirements and achieve a reasonable level of performance across IIoT systems. Radio resource management (RRM) involves strategies and algorithms that manage radio transmission for reliable service delivery in dynamic and diverse wireless networks.

The fundamental challenge in IIoT wireless communication is cross-technology interference combined with harsh signal propagation conditions in industrial systems. This results in deficient networks performance and service failures regardless of prudent initiatives [172]. One possible solution for interference mitigation is coexistence mechanisms. There are two principal concerns in the design of coexistence mechanisms: interference management and load balancing [173]. Since RRM includes transmission power management, radio resources scheduling, user allocation, and preventive–reactive congestion control, effective RRM procedures could be exploited in coexistence mechanisms to mitigate the interference level. Another possible approach to avoid wireless networks interference is the employment of cognitive radio channel sensing of the ambient

radio environments to detect availability of channels. Subsequently, RRM is performed on the clear channels through optimizing proper channel features for data transmission [174, 175]. In addition to reliable link, RRM involves strategies for controlling power transmission, which is particularly important for IIoT devices working on batteries.

      1.6.1.3 Protocol Interface Design

IIoT involves diverse industrial assets such as manufacturing control systems, industrial process controllers, devices, and components. These controllers and equipment are distributed throughout an industrial site and use both proprietary and open protocols for communication. Basically, proprietary protocols belong to a particular product line within the systems [176, 177, 178], while open protocols are governed by standard organizations and utilized across products. Considering the advent of communication technologies and various protocols for both proprietary and open standards, there are technical challenges in the interconnection of different industrial protocols and assets. This calls for the creation of systems and techniques that integrate different protocol interfaces in manufacturing and industrial processes and that allow the interoperation of devices, equipment, and services from various vendors and operators. In this context, Open Platform Communication-Unified Architecture (OPC-UA¹⁶) is a possible solution that offers interconnection and easy integration of newer standards (wired and wireless) and middleware technologies in Industry 4.0 [179]. Moreover, a communication interface for IIoT is proposed in [180] that provides communication among programmable controllers and devices for operating and monitoring processes and equipment.

Design of protocol interface could be discussed in horizontal and vertical directions [55]. Figure 1.1 indicates the concept of integration in Industry 4.0. Typically, horizontal protocol interfaces provide interconnectivity among nodes to meet certain network functionalities such as clock synchronization among nodes. Time-sensitive network (TSN) protocols are examples of such interfaces that provide real-time connectivity for mission-critical and time-sensitive use cases [162, 181]. On the other hand, vertical protocol interfaces assist in secure data and service integration and offer consistent information flow via protocol stacks [55]. IETF has released encapsulation and compression techniques that unify such operations for devices [182]. 6LoWPAN is an example of networking technology from IETF that determines fragmentation mechanism for IPv6 headers [183].

      1.6.2 Metrics for Wireless System Design in IIoT

      The autonomous communication in the future IIoT environment significantly relies on wireless networks. There are different wireless technologies competing with each other for various industrial services and use cases. Since network connectivity should be robust and efficient, crucial challenges are raised in network design and integration of automation and control systems. Furthermore,