# Trends in LPWAN Technologies for LEO Satellite Constellations in the NewSpace Context
## 3 Architectures and Protocols for IoT Communications via Satellites  
### Architecture  
The IoT satellite communications stack model comprises five main layers that work together to collect and process data. The layers are:  
* Physical layer: In this layer, the data are collected from the environment using IoT nodes with sensors, and the environment is controlled through actuators using wireless connectivity. * Gateway layer: This layer consolidates data transmissions from IoT nodes. It includes satellite and terrestrial IoT gateways performing functions as communications gateways of the IoT nodes. A communication gateway is a hardware or software component that serves as an intermediary facilitating data exchange between disparate systems, networks, or devices. It plays a vital role in translating and managing communication protocols, ensuring compatibility and smooth data transfer between devices operating on different technologies or standards, as in IoT satellite communications. * IoT network layer: This layer transports and transmits data to the middleware layer. This consists of the satellite network between the IoT nodes with the satellite, between the satellite and the ground station, and the terrestrial network between the ground station to the operator's cloud and from the operator's cloud to the business applications. * Middleware or IoT platform layer: This layer receives the data transmitted by the IoT nodes and manages their processing. This consists of servers that act as middleware or IoT platforms, typically hosted in the operator's cloud that process, store, and forward satellite data to external applications. * Vertical or business application layer: This layer uses the data received from the middleware layer to achieve a specific goal or purpose. They are applications that analyze and process data for specific business purposes. The satellite IoT communications architecture for physical components is shown in Figure 2 and includes the following elements: \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Aspect** & **Satellite IoT Communications** & \multicolumn{1}{c}{**Traditional Satellite Communications**} \\ \hline Number of connected devices & Scalability to support a large number of IoT devices scattered in different locations. & Less concern about the number of devices, with a focus on the quality and quantity of data transmitted per user. \\ \hline Flexibility and configurability & Greater flexibility to adapt to different protocols and specific requirements of IoT devices. & More robust and specialized configuration to manage different types of telecommunications services. \\ \hline Cost & Emphasis on cost-effective solutions to enable widespread adoption of IoT devices. & Higher budgets, as traditional satellite communication services, require a more complex infrastructure and powerful equipment. \\ \hline Orbit type & Generally, LEO facilitates direct communication with IoT devices and reduces latency. & GEO or MEO to provide constant coverage over specific areas or regions of the planet. \\ \hline Hardware components & Specialized transceivers and antennas for efficient communication with IoT devices. & More powerful communication equipment, including transponders, power amplifiers, and high-gain antennas, for long-distance signal transmission and reception. \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._* IoT nodes: These devices, including sensors and actuators, facilitate wireless communication with satellites. Typically battery-operated, they can connect wirelessly to the satellite network and, in some cases, are compatible with terrestrial networks. IoT nodes are part of the physical layer in the IoT satellite communications stack model. * Terrestrial IoT gateways: These gateways facilitate wireless communication for IoT nodes unable to transmit data to the satellites directly. They forward the data from the IoT nodes, facilitating the relay of data from the ground to satellites.