# Seamless 5G Multi-Hop Connectivity Architecture and Trials for Maritime Applications
## 1 Introduction  
The exploitation of oceans can enable huge economic growth, job creation, and innovation. For example, Ref. [1] showed that, by 2030, the contribution of the marine economy to global value added will be in the range of US$3 trillion, creating about 40 million jobs in the process. The maritime sector is frontrunning regarding digitalization and onboard information and communication technology (ICT) usage onboard. Major technical inspections (class renewal), typically carried out every five years, are often used for the substantialmodernization of ICT systems. However, radio communication, besides analogue voice, satellite and WiFi, has only received limited attention until now. Fifth generation (5G) and sixth generation (6G) mobile communications bear the promise of rolling out seamless connectivity over the sea with a direct impact on the quality of life and quantity of service for labor forces involved in shipping and logistics. A major legislation push towards a new era of digitalization is forcing the maritime cluster to adapt to the new situation. EU initiatives such as the European maritime single window, which applies from 15 August 2025 [2], and the EU single-window environment for customs [3], which made its way into EU law in December 2022, will push digitalization in maritime industries, and, at the same time, these EU acts will increase the need for data and data exchange. The technologies of 5G and 6G fit naturally as enabling technologies: their wide fit-for-purpose radio spectrum and their enabling of customer-oriented features are the means to tailor these requirements. However, despite the recent advances in communication networks on land, offering dependable and high-speed data rates for marine communication remains challenging. The use of an air/space segment in mobile networks has recently gained a lot of attention as one of the solutions to tackling this challenge. For example, there have been recent works in the literature that have addressed this, mostly from a theoretical perspective. For example, in [4], unmanned aerial vehicles (UAV) were considered for the enhancement of the coverage of a hybrid satellite-terrestrial maritime communication network. This setup resulted in a difficult optimization problem, for which the authors proposed a method to solve it. Similarly, the authors of [5] studied the design of a space-air-sea non-terrestrial network (NTN) for energy-efficient resource allocation. Their goal was to maximize the system's energy efficiency by collaboratively optimizing different parameters such as user equipment association, power control, and UAV deployment, which was also formulated as an optimization problem and solved in the paper. From a more practically oriented perspective, the emergence and adoption of new production, propulsion and launching technologies for satellites has drastically reduced the deployment costs of space-based infrastructures and has made mega-constellations viable. Consequently, the use of satellite communication technology as a complement or even an inherent part of future network infrastructures is becoming increasingly interesting for various vertical markets and mobile network operators. The main standardization body for 5G/6G mobile networks, 3 GPP, has already mandated in its Release 15 Service Requirements specification [6] that \"The 5G system shall be able to provide services using satellite access\". With Release 17, which was finalized by mid-2022, the integration of satellites/NTN into 5G mobile telecommunications systems has now been included in all the relevant specifications. According to the Rel. 17 Service Requirements [7], a 5G system with satellite access shall support:  
* \"Service continuity between 5G terrestrial access network and 5G satellite access networks\"
* \"Different configurations where the RAN is either a satellite next generation (NG-) RAN or a non-3 GPP satellite access network, or both\", and also with satellites being part of the transport network.