# Performance Evaluation of Random Access Methods for IoT-over-Satellite
## 2 Background and Related Work  
Depending on various trade-offs related to spectral efficiency, system complexity, and energy usage, different IoT-over-Satellite architectures are investigated. For example, the 3 GPP defines two IoT-over-Satellite methods for mMTC applications using shared frequency bands [9]; these two methods rely on (i) direct satellite access and (ii) hybrid access. In direct-access networks, IoT devices send their payloads directly to a satellite,where satellites act as an intermediate node that relays the data to the destination via feeder link, where Figure 1 depicts this concept. Since IoT devices can connect to the satellite directly without any terrestrial gateways, this makes such topology ideal for rural areas where the terrestrial infrastructure is lacking. Suggestions for IoT-over-Satellite networks that rely on direct access can be found in research papers [18; 21], where [21] illustrated the performance of direct to satellite IoT networks using LoRa based on the simulation, and [18] explores the potential possibilities of spectrum-sharing between LEO satellite constellation and terrestrial networks. On the other hand, hybrid satellite networks allow IoT devices to communicate via either the terrestrial or satellite infrastructure. Both the terrestrial and satellite networks are coordinated to facilitate hand-over between them to ultimately providing seamless global coverage. Thereby, the hybrid satellite system can combine the advantages of both terrestrial and satellite networks, providing global coverage while maintaining more efficient communications in suburban and urban environments. Figure 2 shows the architecture of the hybrid satellite network. In order to allow inter-operation between satellite and terrestrial networks, adapting terrestrial LPWAN directly to the IoT-over-Satellite system is currently being investigated with some promising implementations [8; 18; 22; 23]. To estimate the quality of service (QoS) provided by the communication link, analysis of IoT-over-Satellite systems under different LPWAN communication protocols provides insight into the performance of the system. Analysis of IoT-over-Satellite using licensed band LPWAN technology can be found in [24], where the uplink performance of Narrowband IoT (NB-IoT) over satellite system is presented, showing the feasibility of using terrestrial NB-IoT technology for the satellite applications. Moreover, the performance analysis of the satellite uplink using LTE technology is also presented in [25]. Alternatively, the performance of the unlicensed band LPWAN protocol is investigated in [26], in which the LoRa derivative over a geostationary satellite link is measured using both extensive simulations and test-bed measurements, while in [27], the author used auto-correlation and cross-correlation in the time and frequency domains to investigate the acquisition performance of different types of chirp signals, showing the potential of chirp-based systems on LEO communication links. As next generation wireless systems emerge, more services are occupying the shared spectrum frequently. This is exacerbated from the satellite's perspective where all devices within its footprint can contribute towards interference. In terrestrial networks, spectrum  
Figure 1: Illustration of the direct satellite access IoT network architecture. Figure 2: Illustration of the hybrid IoT-over-Satellite network architecture. regulators continuously set strict regulations to the shared spectrum to reduce transmission congestion. The same is extended to geostationary satellites where spectrum regulators from the different countries covering a fixed footprint. However, LEO satellites are rapidly orbiting and continuously changing their footprint, therefore, more efforts are required to properly regulate the shared spectrum for LEO constellations [19]. IoT-over-Satellite networks are expected to employ random access methods, in a way or another, similar to IoT terrestrial networks [8].