# Open Radio Access Networks For Smart IoT Systems: State of Art and Future Directions
###### Abstract
As a result, it is an appealing solution for network operators and infrastructure providers [30]. The monolithic nature of RAN components, which supported a few vendors and were viewed by operators as black boxes, gave rise to drawbacks such as network node cooperation restrictions, poor reconfiguration, and vendor lock-in [28]. Furthermore, O-RAN technology advocates for the disaggregation of the RAN into smaller modules: a radio unit (RU), distributed unit (DU), control unit (CU), and opening the interfaces between the different components to promote flexibility, interoperability, innovation, and reduce costs [31]. The O-RAN Alliance is a group of companies formed to develop and promote the O-RAN concept. The alliance includes numerous companies, including mobile network operators, equipment vendors, and software providers. The alliance has developed a set of specifications and reference architectures for O-RAN, which are designed to ensure interoperability between different vendors' equipment [32]. Even though the O-RAN idea was initially conceived to support traditional mobile networks, next-generation wireless networks and smart IoT systems are also covered [33]. For example, networks for IoT systems comprise a heterogeneous and growing number of devices, sensors, objects, and other components, which makes it challenging to manage and orchestrate the network. With the aid of O-RAN, the interface between the different network components can be standardized and opened for easier management and orchestration, leading to enhanced efficiency and cost savings. Furthermore, it can facilitate the development of open and standardized interfaces between IoT devices, gateways, and the edge and cloud to allow different vendors' devices and gateways to work together seamlessly. Similarly, O-RAN can promote the development of enhanced edge intelligence solutions, i.e., by processing data close to where it is generated for transmission latency reduction [34; 35; 36; 33]. In this study, we have systematically reviewed the literature by querying the reputable research databases using AND operation between keywords to have precise results such as 'O-RAN' and 'IoT', 'O-RAN' and 'Transportation', 'O-RAN' and 'Healthcare', 'O-RAN' and 'Energy'. Furthermore, the articles are scrutinized to ensure that the O-RAN concept supports the IoT systems conceptually or technically. Articles not satisfying the above criteria are not included in this research. Table 1 lists the key terms and abbreviations in the paper. Our major contributions to this paper are as follows. * We systematically review the applications of O-RAN in smart IoT systems, i.e., transportation, industry, healthcare, and energy. * We propose a generic three-dimensional problem space that considers IoT systems (e.g., transportation, industry, healthcare, energy), targets (e.g., reliable communication, real-time analytics, fault tolerance, interoperability, integration), and artificial intelligence and machine learning (AI/ML) schemes (e.g., reinforcement learning (RL), deep neural networks (DNNs). * We outline future research directions concerning robust and scalable solutions, interoperability and standardizations, privacy, and security. We also present a taxonomy to unveil the security threats to emerge from the O-RAN-assisted IoT systems and the feasible directions to address those threats. The remainder of this paper is organized as follows. Section 2 introduces the background of traditional radio access networks (RAN), the concept of O-RAN technology, AI/ML, and a brief literature review on O-RAN. Section 3 explores the O-RAN in smart IoT systems based on our defined problem space. Section 4 presents several challenges and future research directions. Finally, Section 5 gives the final remarks.