## 3 Overview of 6G Technologies
### Key 6G Features  
6G networks aim to go beyond the enhanced mobile broadband (eMBB), massive machine-type communications (mMTC), and ultra-reliable low-latency communication (URLLC) introduced by 5G toward a fully intelligent, adaptive, and immersive communication system. Below, we present the main features of 6G, the gaps they address, and the expected benefits.  
1. **THz Communications**[47]: THz bands promise to overcome the bandwidth limitations of existing mmWave systems by enabling ultra-high-speed links with terabit-per-second throughput and microsecond-level latency. This is especially useful for short-range, high-data-rate applications such as UAV-to-ship or UAV-to-HAP transmissions in dense maritime scenarios.
2. **AI-Native Network Architecture**[48]: Unlike 5G, which relies on external AI-based management tools, 6G is envisioned to have intelligence built into its core. This allows for real-time self-optimization, predictive resource allocation, and autonomous fault management--key requirements for supporting highly mobile and infrastructure-sparse maritime environments.  
3. **RIS-assisted Propagation**[49]: RIS technology introduces intelligent, reflective surfaces that can manipulate signal propagation to enhance coverage and signal strength. Deployed on UAVs or buoys, RIS can dynamically compensate for NLOS conditions and improve energy efficiency across maritime links.
4. **Integrated Sensing and Communication (ISAC)**[50]: By merging radar sensing and communication into a unified system, ISAC allows maritime platforms to simultaneously detect, track, and communicate. This dual capability can support object avoidance, environmental awareness, and seamless data exchange with minimal spectrum overhead.
5. **Ubiquitous Connectivity via Non-Terrestrial Networks (NTNs)**[51]: 6G integrates satellites, UAVs, and high-altitude platforms to create a truly global network fabric. For MCNs, this ensures reliable communication even in remote oceans, polar routes, and disaster-struck zones where terrestrial infrastructure is unavailable or inoperable.
6. **Blockchain and Post-Quantum Security (PQS)**[52]: To meet the growing demand for secure and tamper-proof maritime communication, 6G will incorporate blockchain for decentralized trust and post-quantum cryptographic algorithms to resist emerging threats from quantum computing.
7. **Digital Twins for Network and Platform Optimization**[53]: 6G enables the real-time synchronization of physical maritime systems such as ships, sensors, and networks--with their virtual counterparts. These digital twins can be used for predictive maintenance, energy optimization, and operational simulations, significantly enhancing situational awareness and decision-making.
8. **Joint Communication and Compute Co-Design**[38]: Rather than treating communication and computation separately, 6G co-optimizes them to reduce latency and improve reliability. This is particularly advantageous in MCNs, where real-time edge intelligence onboard ships or UAVs is necessary to reduce dependence on delayed satellite links.
9. **Maritime Integrated Access and Backhaul (mIAB)**[54]: IAB allows the same radio infrastructure to provide both user access and backhaul connectivity, reducing reliance on wired or dedicated satellite backhaul links. When extended to the maritime domain, mIAB enables dynamic relaying and flexible extension of 5G coverage using vessels or UAVs as intermediate nodes that perform both access and forwarding functions. As discussed in [54], mIAB can be particularly effective in port environments or offshore clusters, where deploying fixed infrastructure is impractical. This mechanism supports scalable, low-cost deployment and may serve as a bridge toward full 6G coverage over oceans by improving network densification and connectivity in coverage-limited zones.