# Integrating Blockchains with the IoT: A Review of Architectures and Marine Use Cases
## 2 Architectural Foundations of IoT, Blockchains, and MIoT/IoUT
### Overview of MIoT and IoUT Systems  
The MIoT extends IoT technology into marine environments, aiming to enable the comprehensive monitoring and systematic management of ocean-related data [24]. These systems are designed to collect marine parameters using underwater sensors and transmit the data to observation systems or cloud platforms, which, in turn, analyze them in detail to improve the management and conservation of marine resources. Research on underwater sensor  
Figure 2: Blockchain architectural layers. networks has been ongoing for years, with early studies such as that by [PERSON] et al. (2018) demonstrating their potential for marine monitoring and communication. The IoUT is a subset of the MIoT that specializes in deploying underwater sensors to continuously monitor oceanic ecosystems, playing an essential role in the development of smart oceans ([PERSON] and [PERSON], 2018; [PERSON] and [PERSON], 2018). However, the complexities of underwater communication--such as ensuring secure data transmission, maintaining data accuracy, preventing sensor corrosion, enhancing energy efficiency, and improving network reliability--pose several challenges that still require more effective solutions. All of the above underscore the need for ongoing research to provide solutions and address the unique demands of the IoUT environment (as will be discussed later in this section) ([PERSON] and [PERSON], 2018). In their research, [PERSON] and [PERSON] (2018) highlight several specific system requirements that differentiate the MIoT--and, by extension, the IoUT--from traditional IoT systems. Firstly, the different types of components utilized in marine and underwater environments entail the establishment of flexible communication methods, such as acoustic links, in order to enable effective communication between underwater robots, surface vessels, buoy systems, and UAVs. In contrast, traditional IoT systems mainly rely on radio waves for communication. Secondly, given the varying bandwidth capabilities of different communication channels in underwater and surface environments, it is essential to develop models that efficiently manage information exchange across these system elements. For instance, [PERSON] and [PERSON] (2018) argue that localization techniques (methods used to determine the geographical location of devices or objects) in the MIoT might rely on directional beacon (LDB) schemes. At the same time, the IoUT might face additional challenges in precise localization due to underwater signal limitations. In contrast, traditional IoT systems often use GPS (Global Positioning System) satellites for positioning. Thirdly, the computational constraints of onboard processing systems in both the MIoT and IoUT present significant challenges that must be addressed through efficient data handling solutions, mainly since battery recharging or replacement is often impractical in underwater settings. Fourthly, the need for low power consumption, along with the challenges of energy generation and storage, collectively highlight the importance of incorporating energy-efficient measures into the MIoT and IoUT system architecture. This includes underwater energy-harvesting technologies such as piezoelectric harvesting (which generates electricity from mechanical pressure) or ocean thermal energy, which are better suited for these environments than traditional IoT energy solutions. Finally, the harsh conditions of marine and underwater environments require highly reliable equipment. Sensors and actuators, as well as other components in the MIoT and IoUT, must be highly watertight to protect them against water, pressure, and corrosion, ensuring reliable operation. Additionally, auxiliary devices such as buoys and mooring systems are essential as they ensure stability and durability, especially given the low network density and high deployment costs of the MIoT and IoUT compared to the denser and cheaper networks of the traditional IoT.