# Performance Modeling Framework for IoT-over-Satellite Using Shared Radio Spectrum
## 2 Background and Literature Review
### IoT Spectrum Sharing  
Conventional Very Small Aperture Terminal (VSAT) access had been using higher frequency bands such as Ku and Ka-band for many decades to meet the growing capacity requirements and to reduce congestion in the spectrum. Those bands require directional parabolic or patch antennas and careful alignment. Due to the high-directivity, frequency-reuse is quite common in these bands, allowing efficient utilization of the spectrum. On the contrary, Land Mobile Services (LMS) usually utilize the L-Band spectrum with less-directional antennas on the terrestrial terminal [4], allowing mobility without the need for a mechanically steerable antenna. However, for global LMS to function, it requires an exclusive license to use across different terrains and countries, which is quite costly and administratively challenging. As an extension for LMS, IoT-over-LEO Satellite is suggested by international organization 3 GPP (3 GPP: Third generation Partnership Project coordinating major cellular technologies are standardized) to enable easy deployment and compact devices [4]. Sharing terrestrial bands with satellite IoT access becomes an attractive option because of the reduced spectrum fees and faster access to the market. This has captured the attention of 3 GPP that is currently working to extend the cellular network to hybrid terrestrial-satellite services. In the 3 GPP technical report [8; 9], various types of IoT-over-Satellite enabling 5G network architectures and the solution of terrestrial-to-satellite network integration in 5G had been suggested. Furthermore, a 3 GPP task force has been working on satellite-to-NB-IoT integration [17]. While 3 GPP systems operate in the licensed spectrum, it is interesting to explore the use of a license-free spectrum, such as the ISM band for shared terrestrial-satellite access use. ISM-band has harmonized standards in many countries around the world, which allow license-free devices to operate within specific parameters; such as the maximum equivalent isotropic radiated power (EIRP), power spectral density, and maximum time-on-air. Therefore, the impact of terrestrial interference on the IoT satellite becomes a major concern in the IoT-over-Satellite system. In Reference [18], the satellite uplink transmission with terrestrial interference is analyzed, assuming an LTE terrestrial network extended by satellite communication using Quadrature Phase Shift Keying (QPSK) or 16--Quadrature amplitude modulation (QAM) modulation with all terrestrial users transmitting at \(-2\) dBm EIRP, and they simulated the uplink SINR level of an LEO satellite showing that communication service can be provided when the number of terrestrial users is less than one million. IoT-over-Satellite communication using the shared ISM band is anticipated to face a massive terrestrial interference in the uplink due to its wide adoption. For example, our previous study in Reference [19] shows that ISM-band 915-928 MHz in Melbourne, Australia is highly congested with spectrum occupancy of around 16%. This figure is quite high for random access systems such as ALOHA, where the normalized spectrum utilization in urban environments is around 40% when considering ALOHA-like access. Since satellites would have a higher probability of Line-of-Sight (LoS) and a wider footprint, the terrestrial interference in the ISM band is expected to be much higher than the terrestrial interference [10].