## 5 IoRT Systems Based on Space-Borne NTN Networks
### Enhanced Data Transmission Reliability  
Researchers in [103] examine the importance of satellite Machine Type Communication (MTC) in the maritime IoT and highlight the challenges hindering its implementation. Their focus is on investigating potential interference issues between a satellite MTC system for maritime IoT and co-frequency terrestrial communication systems already in operation. The main obstacle stems from the lack of established regulatory criteria and methods to safeguard terrestrial systems against potential interference from LEO satellite systems or similar technologies. This absence makes it challenging to assess the impact on existing land systems. The researchers contribute significantly by mathematically deriving an electromagnetic Power Flux Density (PFD) mask. This mask helps evaluate and limit satellite space station emissions within the existing regulatory boundaries designed for mitigating interference among terrestrial communication systems in the same frequency band. The principle guiding this approach is ensuring that the interference experienced by a land system due to a space station is no more severe than that from a co-frequency land system permitted by regulations. \begin{table}
\begin{tabular}{p{56.9 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Ref.** & **NTN Architecture** & **Description** \\ \hline
[95] & GEO & Development of a spectrum management scheme for human-to-human and machine-to-machine communications to improve spectral efficiency, throughput and fairness index. \\ \hline
[96] & LEO NB-IoT & Development of a resource allocation scheme to mitigate the issue of high differential Doppler among terrestrial user channels. \\ \hline
[97] & Nano-satellites & Precise beamforming directed towards specific IoT devices enhances received signals while minimizing interference. \\ \hline
[98] & LEO & Development of a slotted random access protocol based on Walsh codes for a satellite IoT scenario with sink nodes that aims to improve the throughput of the system, especially under high load. \\ \hline
[99] & GEO & Development of a geographical non-orthogonal multiple access-based multiuser beamforming (NOMA-BF) scheme to improve spectral efficiency in multi-beam satellite-based IoT systems. \\ \hline
[100] & LEO & Scheme that combines NOMA and RA technologies for asynchronous transmissions to achieve better throughput performance and an enhanced data transmission rate. \\ \hline
[101] & LEO & Development of a robust multigroup multicast beamforming scheme to improve spectrum efficiency and adequately serve a large number of IoT devices. \\ \hline
[102] & LEO NB-IoT & Development of an uplink scheduling technique for an LEO satellite-based mMTC-NB-IoT system that mitigates the differential Doppler shift, thereby improving the system’s performance in terms of throughput and block error rate. \\ \hline \hline \end{tabular}
\end{table} 
Table 6: IoRT systems based on space-borne NTN networks: **enhanced throughput/transmission rate**. Addressing the challenging link between IoT devices and GEO satellites, a novel modulation and signaling scheme based on Chirp-Spread Spectrum (CSS) is proposed in [104]. This scheme, termed Unipolar-coded CSS (UCCSS), enables reliable transmission at ultra-low bit rates and supports true random multiple access for a large number of devices, even at high carrier frequencies such as C-band to Ka-band. This breakthrough paves the way for ubiquitous connectivity and mMTC via satellite, even in remote and underserved areas. Furthermore, in [105], the same authors further delve into the challenges and opportunities associated with direct access of IoT devices to GEO satellites. They highlight the potential of UCCSS to revolutionize satellite-based IoT communication, enabling reliable and efficient connectivity for a wide range of IoT applications. The successful demonstration of UCCSS with a Ku-band testbed validates its feasibility and opens up exciting possibilities for ultra-narrow band mMTC via satellite.