A Survey on Industrial Internet of Things: A Cyber-Physical Systems Perspective <s> B. I-IOT APPLICATIONS AND CHARACTERISTICS <s> The industrial wireless automation sector exhibits a huge market growth in the last years. Today, many applications already use wireless technologies. However, the existing wireless solutions do not yet offer sufficient performance with respect to real-time and reliability requirements, particularly for closed-loop control applications. As a result, low latency wireless communication technologies will bridge the gap and can become a key factor for the wide-spread penetration of wireless in industrial communication systems. It is therefore the main goal of this paper to provide a comprehensive overview on requirements, current solutions, and challenges as well as opportunities for future wireless industrial systems. Thereby, presented requirement figures, analysis results, and performance evaluations are based on numerous practical examples from industry. <s> BIB001 </s> A Survey on Industrial Internet of Things: A Cyber-Physical Systems Perspective <s> B. I-IOT APPLICATIONS AND CHARACTERISTICS <s> The next generations of industrial control systems will require high-performance wireless networks (named WirelessHP) able to provide extremely low latency, ultrahigh reliability, and high data rates. The current strategy toward the realization of industrial wireless networks relies on adopting the bottom layers of general purpose wireless standards and customizing only the upper layers. In this paper, a new bottom-up approach is proposed through the realization of a WirelessHP physical layer specifically targeted at reducing the communication latency through the minimization of packet transmission time. Theoretical analysis shows that the proposed design allows a substantial reduction in packet transmission time, down to 1 $\mu$ s, with respect to the general purpose IEEE 802.11 physical layer. The design is validated by an experimental demonstrator, which shows that reliable communications up to 20 m range can be established with the proposed physical layer. <s> BIB002
The involvement of industrial applications in IoT makes I-IoT an entirely different world, in meaning and concept, and calls for a deep understanding of term ''industrial''. Thus, we first outline some typical industrial applications and illustrate their characteristics. Industrial applications cover numerous critical production, manufacturing, and transportation systems, including power generation plants, power distribution networks, production facilities and factories, and so on. First, PA is characterized by an industrial process, such as in chemical, oil, and power plants, which are autonomous, i.e., they are controlled and managed with little or no human intervention. A PA system often integrates sensors, controllers, and actuators for information collection, interaction and process actuation. Second, FA leverages robotic systems and assembly line machinery to enable automation of the manufacturing process for the improvement of productivity and efficiency. For example, the robotic arms typically have similar appearance and actuation to their human counterparts, and are able to perform the functions as a human operator, but with greater robustness, productivity, precision and efficiency. With the same objectives, assembly lines often decompose complex tasks into smaller subtasks and perform step-by-step operations according the designed workflow  - BIB002 . An example of PA is power system automation (PSA), which aims to conduct automatic control, monitoring, and protection of power generation, distribution, and usage systems by various instruments and control devices. PSA contains three key components: data acquisition, remote monitoring, and control. The data acquisition is used to collect data from various sensing and control devices, which can be processed either locally or in a data center. Remote monitoring, which is used to monitor the status of the power systems, alerts the operation center to abnormal situations and prevents blackouts. Finally, PSA control plays the role of operating power systems, controlling substations from the operation center. There are several key characteristics associated with industrial applications. The first characteristic is the cycle time, which means the time required to receive commands from the control center and send sensor data to the control center. The cycle time can depend on the I-CPS application. For example, the cycle time for PA is on the order of hundreds of milliseconds. The second characteristic is the number of nodes, which indicates the size of the system (i.e., the number of nodes covered by one controller in a working area). The third characteristic, reliability, is characterized as the quality of information transmission, and can be measured using the packet error rate (PER). For instance, a PER of 10 −9 is considered acceptable BIB002 , BIB001 . In addition, industrial applications are primarily concerned with accurate and timely operation and cooperation among numerous sensors and actuators. Hence, the performance requirements are significantly different from those for consumer-oriented IoT applications. Table 2 illustrates the requirements of two types of industrial applications based on their characteristics. Some examples of performance requirements include latency and reliability from the perspective of communication. Latency, as a critical indicator, measures the performance of the data delivery based on the delay requirement. The cycle time indicates the time required for a process cycle, which varies by the particular industrial scenario. To guarantee the timely and accurate operations of I-IoT systems, the network shall have the capability to provide communications so that critical information can be delivered within the cycle time. Finally, reliability is used to qualify the importance of delivering critical information accurately. Highly reliable transmission requirement indicates that information (e.g., control messages) shall be transmitted with extremely low error rate.