# Worldwide Coverage Mobile Systems for
## 1 Introduction
The requirement of global mobile coverage has driven the need for deploying a satellite constellation system to provide worldwide Internet access, especially where terrestrial systems do not, at a low cost. Access to the Internet is poor in rural areas, far from large urban centres, such as in Alaska. In recent years, several initiatives have emerged aimed at deploying constellations of low-orbit terrestrial satellites to provide connectivity and access to online services to the inhabitants of those regions, which will gradually expand the services to other regions [4]. Inclusion and information access policies spread the smart cities' coverage. The use of drones can be highlighted as an example of smart city range applications. They are becoming increasingly popular, despite the regulations which restrict their usage in public areas. Engineers and scientists have identified the potential of drones in civil applications, such as remote sensing, smart cities, surveillance, disaster detection, management and recovery, rescue, patrolling, aerial survey, border security, etc., among several ones. Low-cost and battery-powered drones are unable to cope efficiently with the requirements of computation-demanding applications (e.g., onboard image processing), encompassing real-time data and reliability constraints. One of their main limitations is the communication range when wireless links are used. With the appropriate infrastructure, it will be possible to manage them in areas beyond the city, e.g., in the country. It is expected that new global coverage communication systems will grant this possibility. Currently, companies, such as OneWeb, SpaceX, Telesat, and LeoSat, are planning to use a large number of low capacity LEO (Low Earth Orbit) satellites to provide the world with broadband internet connection [5]. Because manufacturing a satellite for medium or high orbits is very expensive,low-cost air satellites, such as balloons, and mini-satellites flying at the Earth's low-orbit, have recently appeared [6, 7]. Besides, given the small size (volume) and low weight, their cost for launching is low. While (mobile) smartphones for terrestrial communication systems are becoming smaller and smaller (except for screen size), devices that are linked to those satellites constellations are claimed to show reduced size factor too. Even in the case of drones introduced above a low size, low weight, a low-cost antenna is required to avoid heavy and large drones, the need for more powerful engines, and to reduce the overall cost. At this point, it is worthy to mention the massive machine-type communions (mMTC), also known as the Internet of Things (IoT), which are characterized by a low complexity and the availability of extremely cheap devices that are capable of generating and exchanging information. When considering their small size, the traffic generated by these IoT devices can have a significant impact on the network load. Therefore, satellite communications can alleviate network traffic through backhaul, or provide continuity to services in those cases where the terrestrial network does not have coverage. This use case can be divided into two groups depending on the type of application, as it supports the satellite and how the available sensors are distributed over the ground [8, 9, 10, 11]. NB-IoT devices are one of the most promising technologies to support mMTC communications within 5G communications usage scenarios. In the context of an IoT network with global coverage, low orbit satellites (LEO) will play a very important role given the low propagation losses of these links, as well as the low complexity of the devices [9]. In [12], the authors analyse the problem of critical machine-type communications (cMTC), which is one of the key characteristics identified in future 5G communication systems. The authors provide WFs (Waveform) multi-carrier traditions. They identify and analyse a set of indicators to see how this type of system works.