Toward a secure and scalable IoT: a survey of IOTA-based distributed ledger technologies

The increasing adoption of Internet of Things (IoT) systems demands secure, energy-efficient, and scalable solutions capable of supporting mission-critical operations. Traditional blockchain-based Distributed Ledger Technologies (DLTs), however, face limitations such as high energy consumption, poor scalability, and transaction fees, making them less ideal for IoT environments. This paper presents a structured review of IOTA's Tangle, a lightweight, feeless, and scalable DLT designed specifically for decentralized IoT architectures. The study categorizes recent IOTA-based approaches into four key domains: security, privacy, scalability, and energy efficiency. The surveyed literature is systematically classified and analyzed, highlighting the core challenges addressed by each approach. Comparative evaluation reveals the strengths and limitations of current methods in meeting IoT requirements. The findings suggest that while IOTA offers several advantages over traditional blockchains, integrating hybrid and comprehensive solutions remains a promising direction for future research. The paper concludes by outlining open challenges and opportunities for advancing IOTA-enabled IoT systems.