## 1 Introduction  
The Internet of Things (IoT) domain includes a set of rapidly emerging communication, data processing, and insight generation technologies. It involves sensors and actuators of the physical world together with their communication means--sometimes under resource-constrained or environmentally harsh conditions. Furthermore, it involves data preprocessing and aggregation methods both at the network edge and in the cloud. Regarding human-centered, application-specific needs, the overall domain of IoT also includes methods for predictions, classifications, decision making, insight generation, and many more. Eventually, control processes are triggered based on these decisions, which initiate changes in the physical world, completing the working cycle of Cyber-Physical Systems (CPS). IoT integrates appliances, services, sensors, actuators, etc., to offer connectivity solutions [1]. It also helps to improve the system's efficiency by processing the collected data in real time [2]. However, it introduced many issues due to its resource constraints of connected devices and decentralized architecture [3]. IoT covers various application areas that revolve around people's lives, such as the environment, healthcare, agriculture, transportation, and smart home, by revolutionizing surrounding objects to improve humans' lives [4]. IoT requires solutions in many aspects in order to be considered secure, for example, physical security design, key management, client privacy, secure bootstrapping and transmission of data, authentication, and access control mechanisms [5; 6; 7]. Many approaches have been proposed to overcome the previously mentioned issues, such as a centralized server-client paradigm that relies on cloud servers. However, security and privacy aspects are still missing some pieces, and such features can be provided by blockchain technology. We have reached a point for engineering systems where we need to answer both the traditional requirements for system security and safety [8] and the newly arising need for dynamic reorganization capabilities of supply chains and their system of systems [9]. It became inevitable to present a tenable solution that addresses the above-mentioned issues in IoT architecture to guarantee secure data exchange among IoT objects which requires trustless authentication, security, and robustness. Blockchain technology is one of the most trending approaches nowadays; it presents solid and robust features that can be utilized to overcome many limitations in different domains [10]. IoT ecosystem transactions can be managed securely using blockchain technology by eliminating the centralized entity by deploying distributed and public ledgers to allow anonymity in business models [11]. Blockchain enables data integrity and transaction transparency through a decentralized Peer-to-Peer (P2P) model. Many industrial and research domains are expanding their work on top of blockchain technology which results in higher efficiency compared to the traditional manner. An in-depth discussion is described in further sections. Many papers have discussed the concept of blockchain technology and IoT, including systematic reviews, applications, challenges, and solutions such as [12] in general, and furthermore, in [13; 14; 15; 16; 17; 18]. Moreover, further research addresses the integration of blockchain technology and IoT, which is also heading for advanced directions, including industrial and 5G support [19; 20; 21; 22; 23; 24; 25; 26]. This paper will mainly focus on blockchain technology and IoT in a systematic manner to identify new perspectives and serve as a repository for the accumulated knowledge of these technologies in terms of research motivation, issues and challenges, solved gaps, the performance of these technologies in transactions and end devices, answering an important research question to identify the importance of using blockchain technology to boost the performance of IoT, and the usage of hybrid blockchains.