**7. The emergence of 5G in satellite systems**

The fifth-generation technology standard for cellular networks (5G) has been already established on the ground infrastructure as a fast, reliable, and highconnectivity communications interface for cellphones and other devices. The 3rd Generation Partnership Project (3GPP) developed multiple specifications that conform this standard over the years [37] to satisfy the requirements of future usecases. These requirements were presented by the International Telecommunication Union Radiocommunication (ITU-R) sector in the International Mobile Telecommunications (IMT) for 2020 and beyond [38]. The standard presents three usecases according to the current and future telecommunications activity: the enhanced Mobile Broadband (eMBB), the massive Machine Type Communications (mMTC), and the Ultra Reliable Low Latency Communications (URLLC). The eMBB scenario is an evolution of the mobile broadband applications developed in the previous generation standard (4G) by improving the data transfer performance and increasing the seamless experience. Both URLLC and mMTC are new use-cases that were defined due to the emergence of the Internet of Things (IoT) and the apparition of Critical Communications (CC). The IoT paradigm [39] promotes the interconnection of multiple devices that can exchange data without requiring human interaction. In this way, the mMTC represents this trend which is characterized by a myriad of connected devices that typically transmit a relatively low volume of delay-tolerant data. The URLLC scenario is centered on safety and critical applications that require real-time and reliable communications, such as control of industrial manufacturing, remote medical surgery, autonomous driving, and other emergency applications.

The 5G specifications were developed to satisfy the requirements published by the ITU-R in [40]. This development has been conducted to achieve three main goals:


Is in this last goal in which satellites have stood out as a promising platform to be integrated with the 5G infrastructure. In March 2017, 3GPP started new activities to

### *From Monolithic Satellites to the Internet of Satellites Paradigm: When Space, Air… DOI: http://dx.doi.org/10.5772/intechopen.97200*

study the role of the satellites in the 5G [19]. The outcome of these studies was the definition of the Non-Terrestrial Networks (NTN) which encompasses the multiple systems not located on the ground, such as satellites, Unmanned Aerial Vehicles (UAV), or High Altitude Platforms (HAP). This network leverages this high altitude architecture which awards the satellites with unique qualities for the 5G. In this way, the NTN are conceived following the multi-layered satellite network premise, but including in the architecture other systems than only satellites. The large coverage area of spaceborne telecommunications systems enhances the service continuity in case that is not being ensured by ground infrastructure. Furthermore, satellite coverage enhances the network capacity by serving a myriad of end-users with a single spot. Finally, the orbit trajectory of a satellite allows reaching the service ubiquity on the entire globe, being able to provide services in remote and typically inaccessible areas.

These qualities have led to the definition of multiple satellite applications in the eMBB, mMTC, and URLLC scenarios [18]. The eMBB scenario would leverage on satellite systems working as complementary traffic backhauling nodes of the network, or by reducing the handovers of those mobile nodes that perform large trajectories, such as trains or airplanes [41]. Satellites could enhance the services in the mMTC scenario depending on the area in which the devices are deployed. For wide-area services, the satellites play the important role of large visibility to become a central node that feeds device traffic. Otherwise, in local area services, the satellites become a complementary infrastructure to backhaul the traffic of a massive number of devices, like the eMBB case. Unlike the other cases, satellite altitude prevents from achieving the required end-to-end latency for URLLC cases. Nevertheless, the satellites enhance these services by providing a supporting role that broadcasts information over a wide area.

Novel private entities have observed this potential capacity of satellites to support the current 5G and IoT infrastructure, and they started the development of their satellite constellations. Lacuna Space started the development and launch of a dedicated CubeSat constellation for supporting IoT services from space [42]. Currently, they have just launched the third satellite of the constellation which uses Long Range (LoRa) communications technology. Other companies like Sateliot, Kepler Communications, or Eutelsat have also pronounced to deploy their constellations. It seems that another space race started to integrate satellites into the IoT paradigm.
