# Trends in LPWAN Technologies for LEO Satellite Constellations in the NewSpace Context
## 2 Satellite Constellations in IoT  
Artificial satellites serve various functions, such as communications, Earth observation, navigation, and global positioning. However, a single satellite cannot provide global coverage simultaneously. To address this, satellite constellations, which consist of numerous satellites, have been developed to enhance coverage and ensure global reach [15]. A satellite constellation is a group of satellites working together under centralized control to achieve a common objective [19]. Positioned in complementary orbital planes and connected to global ground stations, these constellations aim to provide interconnected network capabilities for IoT communications. This design ensures that at least one satellite is visible in specific Earth regions, offering continuous coverage. Each satellite has a specific role in an IoT communications constellation, collaborating to offer comprehensive global services. Utilizing advanced communication technologies, they connect with Earth-based users through various antennas, such as directional antennas, omnidirectional antennas, and satellite dishes, adapting to different used cases and environmental conditions. Advanced orbit control technology keeps satellites in the correct position in space. This involves the continuous monitoring of satellites from Earth and necessary adjustments to maintain their proper orbits [20]. Satellites in these constellations are strategically placed in different orbits, each optimized for specific tasks. The orbits, shown in Figure 1, include:  
* Low Earth Orbit (LEO): Satellites in LEOs are located at altitudes between 160 to 2000 km above the Earth's surface. These satellites can provide constant global coverage due to their proximity and ability to orbit the Earth multiple times daily. They are primarily used for Earth observation, communication, and global positioning services. * Medium Earth Orbit (MEO): Satellites in MEOs are located between 2000 and 35,786 km above the Earth's surface. They provide regional coverage and are typically used for satellite mobile telephone services, navigation, and global positioning. * Geosynchronous Equatorial Orbit (GEO): Satellites in GEOs are positioned at a constant altitude of around 35,786 km above the Earth's surface and move at the same speed as the planet's rotation. This allows them to stay in a fixed location relative to a specific point on Earth. Communication and meteorological observation services primarily use this region for uninterrupted coverage. While advantageous for their reduced transmission power and ability to utilize smaller satellites, like CubeSats, LEO satellites face challenges. These include more satellites to cover larger areas and the Doppler effect impacting communications [21]. These challenges imply additional costs and complexities in designing and operating satellite communication systems. Satellites are classified based on their application, orbit, and mass. The mass-based classification is the most common method (as shown in Table 1) due to its importance in determining the development and launch costs [22]. Large satellites have a useful lifespan of up to 10 years. They are designed for long-term operations, with redundant systems and electronic components resistant to space and cosmic radiation. They require more energy, which is generated by large photovoltaic solar panels. Due to their size, they are more complex to launch and require more powerful propulsion systems [22]. Figure 1: Types of orbits based on their orbital distances. The trend towards smaller, more affordable satellites is on the rise. Minisatellites weighing between 100 and 500 kg are becoming a popular alternative to large, expensive satellites. The miniaturized electronics in these satellites make them smaller and lighter, providing redundancy to ensure reliability. This miniaturization also reduces the launch costs, making it easier to launch them.