## 4 Related Work
According to a study by [PERSON] et al., Hyperledger Fabric (HLF) is a widely used blockchain platform that offers permissioned blockchain services [21]. The study focuses on identifying performance bottlenecks of HLF in IoT systems, as HLF is hosted by the Linux Foundation. The authors emphasize that the scalability limitations of HLF can result in performance issues in the system [21]. The study highlights that large-scale distributed ledger systems like HLF present various research challenges, such as throughput, latency, network size, and data transfer rates [21]. The authors evaluate the scalability and propose a blockchain-based framework for large-scale IoT systems [21]. According to the authors, blockchain applications have merged with IoT and communication technologiesto create sensor-based systems on a large scale, including air quality monitoring [21]. The authors also mention that blockchain offers promising protection for availability, confidentiality, and integrity, but integrating blockchain and IoT technologies poses challenges [21]. The authors contribute to showcasing the importance of Distributed Ledger Technologies (DTL) and enhancing the cryptographic primitives of DTL systems. Additionally, they evaluate blockchain-based plugins and HLF payment transactions [21]. The issue of network scalability of blockchain on sensor networks with low-powered devices has not been researched in any depth. According to [PERSON] et al., decentralized blockchains have been widely used for IoT systems to secure data management [22]. As the authors emphasized, most existing works have ignored user privacy, which can cause severe privacy issues. As per the authors, privacy concerns may limit the wide use of IoT systems in any domain [22]. The authors have proposed a Policy-hidden Fine-grained Redactable Blockchain (PFRB) solution to cover the research gap [22]. This solution allows users to match the existing blockchain policies and policy contents. As the authors have highlighted, PFRB is successful against plaintext attacks. The authors have used the Policy-based Chameleon Hash technique (PCH) to design the PFRB [22]. Also, the authors have emphasized the practical use case scenario of PFRB in smart healthcare systems. According to [PERSON], Distributed Ledger Technologies (DLTs) represent a new digital ecosystem that can be a possible solution for limitations in traditional cyber-physical systems [23]. Authors have investigated the scalability limitations of different blockchain networks, including Bitcoin, Hyperledger Fabric, Multichain, and Ethereum. As the authors have emphasized, the throughput of different blockchain networks varies based on their architecture [23]. Also, the response time of blockchain networks can be over 500 s. According to the results of the paper, the throughput of some blockchain networks may reach 660,000 blocks per second, while others reach 3-5 blocks per second [23]. According to [PERSON] et al., IoT has become pervasive in day-to-day life. As the authors have highlighted, the protection of smart devices and their autonomy are the most significant challenges [24]. However, researchers have identified the blockchain as a possible solution to address those concerns. In this paper, the authors have proposed a two-tier blockchain framework to enhance the autonomy and security of IoT smart devices. The authors have grouped the IoT smart devices into two groups [24]. The first-tier blockchain operates locally, while the second-tier stores transaction values. The authors have considered smart home contexts with lower physical space and criticality. The authors have used suitable trust and reputation-measurement techniques to assess the reliability of IoT smart devices [24]. Also, the authors have used blockchain technology to certify transactions and to identify the anomaly behaviors of smart objects. The first tier implements a local IoT solution, while the second tier concerns the whole global IoT system.