## 5 IoRT Systems Based on Space-Borne NTN Networks
### Enhanced Throughput/Transmission Rate
The research in [99] explores a Non-Orthogonal Multiple Access-based multi-user Beamforming (NOMA-BF) scheme for improving spectral efficiency in satellite-based IoT. The proposed scheme has been developed for scenarios in which primary users are prioritized with timely data transmissions and guaranteed data rates, while secondary users are opportunistically served. To reduce inter-beam interference, improve effective channel gains, and optimize inter-beam power allocation, the scheme employs a multi-layered beamforming strategy. Numerical results demonstrate that the proposed scheme enhances spectral efficiency while meeting user data rate requirements. The research work in [100] emphasizes the potential of the upcoming 6G standard to provide seamless IoT network coverage by 2030. Underscoring the importance of satellite-based communications in meeting IoT service requirements in the 6G era, this study analyzes in depth the multiple access technologies required for effective satellite-based IoT deployment. It includes information-theoretic considerations and key technologies such as NOMA and Random Access (RA). This analysis evaluates how the satellite transmission environment impacts these access technologies. Furthermore, it aims to improve system throughput and robustness under varying traffic conditions by proposing a novel Non-Orthogonal Massive Grant-Free Access (NoMaGFA) scheme that combines the benefits of RA and NOMA for asynchronous transmissions in satellite-based IoT while maintaining low signaling overhead. In response to the growing demand for spectrum-efficient satellite-based IoT systems, ref. [101] introduces a cognitive satellite-terrestrial framework that leverages multibeam satellite capabilities with full frequency reuse. The proposed scheme maximizes the achievable rate while ensuring outage probability and power consumption constraints. To address the complex optimization problem, a two-level iterative algorithm is developed that incorporates Bernstein-typeand large deviation inequality-aided methods for probabilistic constraint handling. Numerical simulations illustrate that the proposed scheme is efficient as well as sensitive to key parameters. The study in [102] identified NB-IoT as a key technology for supporting massive machine-type communication (mMTC) scenarios within 5G networks. LEO satellites offer the potential to enhance the link budget by reducing propagation signal loss, which is crucial for low-complexity, low-power, and cost-effective IoT devices. However, LEO orbits introduce higher Doppler effects, which can negatively impact the performance of IoT communication. To mitigate these effects, the study proposes an uplink scheduling technique for a mMTC-NB-IoT system based on LEO satellites. Numerical simulations are employed to evaluate the performance of the proposed technique and highlight the limitations imposed by the satellite channel. Table 6 presents a concise summary of the information presented in this section. Various techniques, such as efficient spectrum management, beamforming, and NOMA, are employed to achieve significant improvements in data transmission rates. These techniques address the challenges posed by large-scale IoT deployments, paving the way for future IoT systems that can support massive connectivity.