# Trends in LPWAN Technologies for LEO Satellite Constellations in the NewSpace Context
## 3 Architectures and Protocols for IoT Communications via Satellites
### Architecture
\begin{table}
\begin{tabular}{c l l} \hline \hline
**Criterion** & **DtS-IoT** & **ItS-IoT** \\ \hline \multirow{3}{*}{Connection} & Devices connect directly to & Connection through terrestrial \\  & satellites. & infrastructure, such as base \\  & & stations or gateways, which then \\  & & connect to satellites. \\ \hline \multirow{3}{*}{Communication Protocol} & Uses specific IoT protocols for & Can use a variety of \\  & low-power and low-speed & communication protocols, such as \\  & data transfers, like LPWAN & cellular, sensor networks, and \\  & protocols. & LPWAN protocols. \\ \hline \multirow{3}{*}{Coverage} & DtS is suitable for areas & ItS is more appropriate in densely \\  & lacking a terrestrial & populated areas justifying the \\  & infrastructure or where it is & deployment of dedicated IoT \\  & temporarily unavailable. & gateways [31]. \\ \hline \multirow{3}{*}{Cost and Efficiency} & Devices can be more & Can be costly and consume more \\  & cost-effective and efficient as & energy due to a terrestrial \\  & they do not require an & infrastructure and communication \\  & additional terrestrial & through multiple links. \\  & infrastructure. & \\ \hline \multirow{3}{*}{Development and  Deployment} & Can be easier and quicker to & Can require more time and \\  & develop and deploy as they & resources for development and \\  & do not rely on a terrestrial & deployment due to the need to \\  & infrastructure [32]. & build and maintain a terrestrial \\ \hline \multirow{3}{*}{Applications} & DtS is especially useful in less & \\  & accessible regions, like oceans, & \\  & mountains, and poles, where & \\  & deploying IoT gateways can & concentration of IoT devices [33]. \\  & be difficult or unjustified [31]. & \\ \hline \multirow{3}{*}{Latency} & DtS generally has lower & iDtS involves data passing \\  & latency as the data are & through terrestrial gateways \\  & transmitted directly from IoT & before reaching satellites, \\  & devices to satellites. & potentially increasing the latency. \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparative summary between DtS-IoT and ItS-IoT. Figure 3: IoT communication architecture: (**a**) ItS-IoT and (**b**) DtS-IoT. Compared to terrestrial IoT communications, implementing a satellite network in an LEO has significant differences. A key difference is the extent of coverage: terrestrial gateways typically cover only a few kilometers, whereas a satellite in an LEO can cover hundreds of kilometers. This disparity is influenced by several factors, including the satellite's orbital position, the transmission beam's shape and size, its distance from Earth, and the elevation angle, all of which affect the satellite's coverage area [34]. LEO satellites move at high speeds around the Earth, causing the footprint and transmission beam to move across the ground at thousands of meters per second. This generates a negative frequency distortion due to the Doppler effect, resulting in rapid dynamic changes in network connections and the number of service terminals. Additionally, terrestrial IoT nodes have a limited communication distance of several kilometers, while satellite IoT nodes have a signal transmission distance that extends to hundreds or thousands of kilometers. This extended range leads to significant transmission losses and delays, adversely affecting the energy consumption of IoT devices and necessitating specialized design considerations for communication protocols [35]. Cross-cutting any architecture, some authors have proposed improvements in the security and reliability of these communications by including new technologies, such as Artificial Intelligence (AI), Machine Learning (ML), and Blockchain. In this sense, the Machine Learning (ML) algorithms presented allow a more intelligent allocation of resources in satellite networks, dynamically adapting to changing traffic patterns, improving, among other things, average access, and improving congestion in satellite IoT networks [36].