# Integrating Blockchains with the IoT: A Review of Architectures and Marine Use Cases
## 4 Applications and Challenges of Blockchains in MIoT and IoUT
### Challenges in Blockchain-Enabled MIoT and IoUT Systems  
The integration of blockchain technology into MIoT and IoUT environments presents numerous challenges. However, before addressing the specific issues arising from this integration, it is important to recognize the core challenges to these systems, which stem from the inherent nature of underwater environments, that are not directly related to blockchains. First, communication in MIoT and IoUT systems faces significant hurdles. These systems rely heavily on acoustic waves, which are hindered by low data rates and high latency [18]. While optical and Radio Frequency (RF) technologies can offer faster speeds, their effectiveness is limited by short ranges and line-of-sight requirements, which necessitate a direct path between the transmitter and receiver for effective signal transmission. However, in some cases, alternative configurations that don't rely on a strict line of sight can be used [17; 49]. Other methods, such as hydroacoustic and electromagnetic communication, are also utilized, though they come with their own limitations [16]. Additionally, oceanic conditions, such as high pressure variations and shifting currents, which can move nodes and disrupt stable connections, further complicate these communication challenges. Additionally, a major obstacle is the lack of standardization in MIoT devices and protocols, hindering interoperability among various systems and organizations [16; 17]. Current network protocols and standards are often insufficient, especially for marine monitoring applications ([PERSON] and Kramar [16]). Key areas that require standardization include the devices specifically designed for marine environments (e.g., sensors and actuators) and communication network structures, including protocols and algorithms for reliable data transmission in these settings. Additionally, computing and data storage mechanisms--whether cloud-, fog-, or edge-based--and data archiving methods need to be standardized to ensure cohesive operation. Equally important is the standardization of data analysis results and reporting formats in order to facilitate effective data sharing between different organizations and governments [16]. Beyond standardization, ensuring security and scalability in MIoT and IoUT systems is critical. Effectively managing large volumes of oceanic data while securing their transmission from IoUT sensors is essential for maintaining the stability and reliability of these networks [14]. Moreover, the limitations inherent to underwater sensors, such as limited computing power, storage capacity, and energy resources, further complicate these efforts. Additionally, the unpredictable conditions of underwater environments, characterized by network instability, frequent disconnections, and inconsistent sensor throughput, can often result in irregular data transfers, complicating the management and analysis of IoUT data. Along those lines, many of the challenges discussed in this section are specific instances of the broader issues of improving scalability and ensuring the effective operation of these complex systems. Furthermore, energy efficiency is a significant challenge for devices deployed in remote marine settings. More specifically, IoUT nodes face strict limitations on power, processing, and storage, which makes their operations significantly more resource-draining [18]. At the same time, these devices must operate under strict power constraints, making recharging or maintenance difficult. Additionally, harsh conditions such as corrosion and pressure further complicate their operation. Although blockchain technology can help address some of these challenges, its implementation can further complicate them or lead to new ones. One significant issue is the high computational power required by consensus algorithms such as PoW, which can overwhelm IoUT devices with limited computational capabilities [20].