# Blockchain Interoperability for Future Telecoms
## 3 Literature Review  
This study focuses on the current 5G and upcoming 6G requirements outlined in widely cited research papers, where blockchain technologies are expected to play a crucial role in the future. Based on these requirements, interoperability is one of the most essential factors for connectivity in 6G 3D networks. These flexible 3D connections enable  
Figure 5: Network slicing and dynamic spectrum sharing architecture. O-RAN, open radio access network; MNO, mobile network operator; MVNO, mobile virtual network operator; OTT, over-the-top. users to connect seamlessly with air, space, and ground service providers. Blockchain interoperability can effectively address multi-level interconnections. Previous research, including projects based on permissionless cryptocurrency solutions, has shown that such approaches are unsuitable for enterprise domains due to their high security and privacy expectations. The telecommunications domain is even more stringent due to the intense regulatory requirements it faces. Therefore, this study focuses solely on solutions suitable for telecoms within the permissioned blockchain space and explicitly does not aim to provide comprehensive coverage of the literature, as there is already extensive research on interoperability and its coverage. This literature review primarily focuses on a thorough examination of significant research databases, including IEEE Xplore, ACM Digital Library, SpringerLink, ScienceDirect (Elsevier), Scopus, MDPI, IEEE Access, and arXiv, to identify relevant manuscripts related to blockchain interoperability and telecommunications in the context of blockchain technology. The citations for these selected works have been meticulously verified through Google Scholar. Instead of attempting a comprehensive overview of all relevant studies, this review strategically selects the most widely recognized and highly cited research addressing these solutions, along with projects developed by established organizations, such as International Business Machines (IBM). This review covers the most critical design categories and architectural approaches from these projects, research papers, and the literature in general. The scope of this study enables us to demonstrate research directions for the most substantial and suitable solutions using these categories and architectural approaches, including research directions relating to the development of an ideal architecture, particularly for 6G communications. Finally, the carefully selected and reviewed solutions are compared to finalize the review and provide research directions through the selection of the most suitable solution. Finally, the chosen solution is verified to determine whether it meets the expected criteria for an ideal permissioned interoperability solution. Researchers reading this paper should consider this selection as a guide for future research on blockchain interoperability in the telecommunications field. [PERSON] et al. [43] published a literature review focused on the opportunities and challenges of applying blockchain technologies in the pharmaceutical industry. In particular, they discussed five opportunities that blockchain technologies offer: transparency, reduced transaction time, security, cost efficiency, and irreversible transactions. Furthermore, five primary challenges associated with current blockchain technologies were identified, emphasizing the need for solutions to unlock these opportunities: interoperability, scalability, storage, social acceptance, and standardization requirements. These challenges intersect with known issues in the telecom industry, where interoperability is a critical hurdle. [PERSON] et al. highlighted the importance of security, which is essential for telecom cross-chain communication. Achieving technical interoperability does not eliminate security concerns, which remains a complex issue requiring targeted solutions.