**1. Introduction**

Smart technologies play a crucial role in sustainable economic growth. They transform houses, offices, factories, and even cities into autonomic, self-controlled systems without human intervention [1]. This modern automation trend and ever-increasing use of cuttingedge technologies are boosting the world's economy [2]. The Internet of Things (IoT)

**Citation:** Majid, M.; Habib, S.; Javed, A.R.; Rizwan, M.; Srivastava, G.; Gadekallu, T.R.; Lin, J.C.-W. Applications of Wireless Sensor Networks and Internet of Things Frameworks in the Industry Revolution 4.0: A Systematic Literature Review. *Sensors* **2022**, *22*, 2087. https://doi.org/10.3390/ s22062087

Academic Editors: Suparna De and Klaus Moessner

Received: 9 February 2022 Accepted: 2 March 2022 Published: 8 March 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

and Wireless Sensor Networks (WSN) both play vital roles in this modernization [3]. IoT is a branch of engineering primarily concerned with offering thousands of miniature, physical connected objects, which may collaborate to achieve a shared goal. IoT has gained much importance due to the abundant usage of these tiny networked devices. These are smart, ye<sup>t</sup> basic things that can sense and communicate wirelessly [4]. WSN is a collection of sensor and routing nodes, as shown in Figure 1, which may be put together in the environment to predict physical conditions, such as wind, temperature, and many others. These networks collect and process data from tiny nodes and then transfer it to the operators. Figure 2 illustrates that sensor networks are used in a variety of control systems, including environmental monitoring, home automation, chemical and biological assault detection, smart grid deployment [5], surveillance, and many more. WSN also plays a significant role in aquaculture and the oil industry, including data collection, offshore exploration, disaster prevention, tactical surveillance, and pollution monitoring [6–8].

**Figure 1.** Architecture of wireless sensor network (WSN).

**Figure 2.** Application of wireless sensor network (WSN).

WSN are often deployed in remote areas where human intervention is not possible for post-deployment maintenance. Therefore, efforts are being made to enhance their efficiency and durability [9]. There are many barriers to WSN deployment, such as power consumption–long-distance deployment. Due to automation trends and applications developed, these barriers are no longer barriers for large-scale remote deployment. In general, WSN follows a star topology to decrease the network failure probability by connecting all systems to a central node. While ad-hoc networks follow mesh topology where each node is human-driven [10].

In physical production systems, grid and energy-saving applications minimize the energy resources and noise pollution. In the last few decades, transportation has improved a lot with the usage of smart IoT devices, such as signals and high-resolution cameras on roads, which has led to an increase in traffic flow. RFID readers are deployed at toll booths that automatically deduct toll amounts after reading RFID tags on vehicles. In the transportation sector, smart vehicles reduce the travelling time and also fuel consumption with low cost of mobility and reduced human efforts [11], atmospheric monitoring reduces pollution, and surveillance applications reduce crime. Nowadays, WSN also plays a role in precision agriculture. On the other hand, WSN applications facilitate our day to day lives, making them more comfortable, such as healthcare applications that improve our health and longevity.

Besides WSN, IoT has also played an important role in human life. IoT and the digital age play essential roles in overcoming social and physical barriers and providing ease and mobility to people, resulting in improved and equal opportunities, and access to information [12,13]. IoT also has many application areas such as agribusiness, climate, clinical care, education, transportation, and finance, as shown in Figure 2.

In regard to information and communication technology, researchers are attracted to IoT [14]. By adopting this essential technology, companies have become smarter, more competitive, automated, and sustainable in the global supply chain. In today's competitive marketplace, supply chains are struggling as they compete with each other. Therefore, IoT devices are an effective way to authenticate, monitor, and track products using GPS and many technologies [15,16]. Industry 4.0 stands for the fourth industrial revolution in the digital age, it is associated with virtualizing real-world scenarios of production and processing without human intervention. This virtual world is linked to IoT devices, allowing the creation of cyber–physical systems to communicate and cooperate [17,18]. This fully connected manufacturing system—operating without human intervention by generating, transferring, receiving, and processing necessary data to conduct all required tasks for producing all kinds of goods—is one of Industry 4.0's key "constructs". The concept of Industry 4.0 is based on the combination of three main elements: people, things, and business [19]. A complete cyber–physical production system created by the integration of IoT devices, things and objects (IoT), sensor nodes (WSN), and people, is shown in Figure 3. CPS is a typical example of Industry 4.0. IoT is the connection of smart devices, objects, or machines to the internet and with each other. In WSN systems, there is no direct connection of these devices to the Internet. These systems can send their data to the Internet by connecting several sensor nodes to a central routing node. While CPS systems involve the integration of IoT devices, computation, networking, and physical process, IoT is an essential component of CPS. CPS systems are key elements in the implementation of IR 4.0 [20]. Industry 4.0 is the network-enabled entity that automates the whole process of manufacturing, connecting business and processes. Market demands and the advancements in new technologies are transforming manufacturing firms' business operations into smart factories and warehouses. Due to this automation, IoT devices are producing a massive amount of data daily, known as big data [21,22]. Statistics show that, at the end of 2021, there were more than 10 billion active IoT devices globally [23]. By 2030, the number of active IoT devices is expected to exceed 10 billion to 25.4 billion. By 2025, the data created by IoT devices will reach 73.1 ZB (zeta bytes) [24]. In 2020, the IoT industry was predicted to generate more than USD 450 billion, including hardware, software, systems integration,

and data services. By the end of 2021, it reached USD 520 billion. The global amount expected to be spent on the IoT in 2022 is USD 1 trillion. The IoT industry is predicted to grow to more than USD 2 trillion by 2027 [25,26]. The increasing number of devices and the usage by humans shows the importance of IoT devices; moreover, the industry is growing and gaining revenue.

**Figure 3.** CPS system–integration of IoT, wireless devices, and people in Industry 4.0.

In this paper, we conduct a detailed systematic literature review on the applications and contributions of IoT and WSN in Industry 4.0. We had a large corpus of data to analyze papers using systematic approaches. Among the selected articles, we obtained 22 articles describing the detailed review of existing security techniques, applications used, advantages/disadvantages, and limitations of IoT and WSN. Most of them reviewed the articles in terms of application of IoT and attacks only. The paper mainly focuses on research challenges, issues, limitations, and the future direction of IoT and WSN frameworks in Industry 4.0.
