## 2 Enabling Satellites Technologies and Related Works
In [16], a critical overview of the possibility of using NB-IoT over LEO, compliant with 3 GPP specifications, is presented, and a novel service-oriented methodology is offered to design an effective solution, stitched around application requirements and technological constraints. In [17], a comprehensive state of the art of the development of the NB-IoT via NTN is reviewed. It was found that despite increased attention on the issue of congestion in LEO satellite networks, no effective algorithm has been proposed to address it while considering the limited visibility window of the satellites. To improve this, a novel twofold approach is suggested and evaluated with simulations: first, dividing the satellite's coverage area into Coverage enhancement Levels (CLs), with preambles assigned based on user visibility and transmission length; second, a smart backoff algorithm is introduced, allowing users to calculate a customized backoff interval, improving the efficiency of the random-access procedure. The NB-IoT4 Space [18] project funded by the ESA and developed by an Italian team (including CNIT) developed a demonstrator, in which communication between an NB-IoT User Equipment (UE) and an eNB adapted according to the 3 GPP standard for LEO satellite communications was functionally verified. Satielot [19] is the first company to operate a Low-Earth Orbit (LEO) 5G IoT satellite constellation acting as a seamless roaming extension of cellular networks. It will launch four new satellites into space during 2024 with SpaceX [20]. Furthermore, a new launch and deployment services agreement was recently announced with Exolaunch [21]. With the deployment of these four satellites plus the two already orbiting the Earth, Satielot enters the first phase of its constellation, moving towards the impending commercial phase. Looking ahead, Rel-18 and Rel-19 3 GPP will further extend the 5G outreach by including solutions to enable both NR-NTN and IoT-NTN in bands above 10 GHz to serve fixed and moving platforms (e.g., aircraft, vessels, UAVs) as well as building-mounted devices (e.g., businesses and premises) [22]. The goal of these efforts is to further optimize satellite access performance, address new bands with their specific regulatory requirements, and support new capabilities and services as the evolution of 5G continues. Further evolution of IoT-NTN is underway with a dedicated Rel-19 work item, focusing on support of Store & Forward (S&F) operation based on regenerative payload, including the support of feeder link switchover to guarantee the best possible uplink and downlink connectivity, especially in low-density constellations and even when visibility to a ground station is discontinuous [23]. With this innovative feature, IoT delay-tolerant applications can connect from day one and avoid the huge cost of mega-constellations. Finally, again in the context of LEO direct access, mention should be made of Astrocast's network [24], based on a proprietary system developed from scratch together with Airbus and Thuraya, which differs from networks from other satellite providers that are trying to extend existing standards, such as LoRa and NB-IoT. Astrocast already offers a commercial service with global coverage, transmitting in the L-band by operating a constellation of LEO nano-satellites with a highly optimized protocol for IoT in terms of energy consumption and efficiency. Regarding the other approach, i.e., using the satellite link as a backhauling function, a possible architecture was proposed by the so-called \"MegaLEO\" project [25] using three wireless network types--WSN, WLAN, and WWAN--to address maritime transport issues, such as cold chain monitoring, leveraging an IoT network supported by MEO satellites. The communication infrastructure involves Zigbee for WSN sensor networks, WiFi for communication with ship-based stations, and SatCom for satellite connectivity, integrating with the AIS protocol to improve system throughput and reduce latency compared to GEO satellites.