# Multi-Layered Satellite Communications Systems for Ultra-High Availability and Resilience
## 2 Market Analysis and Regulations
### Regulatory Factors for MLSS Systems
In the ITU-R RR [19], GSO and NGSO are usually seen as competing for resources, hence, either the bands are limited to only a certain orbit, or EPFD hard limits and coordination are used to protect GSO links. The main technical solution is for the NGSO to avoid operating when it is interfering with a GSO. Additional considerations and aspects needing further consideration have been listed in [22]. The main issues are regarding the coexistence of GSO and NGSO and the interference created by a large constellation of NGSOs upon GSOsystems or other NGSO systems. It is not yet settled how the limits should be set and a lot of work is ongoing to calculate and monitor this interference and how to mitigate it. However, the scenario in which both NGSO and GSO belong to the same network does not seem to be considered in the regulations or the ongoing activities. If a band is allocated to both GSO and NGSO and both satellite layers follow the hard limits imposed in Article 22 [19], there is no reason to not allow them to coexist, even more so if they are part of the same network. **Satellite-terrestrial coexistence**: One potential way to share the band is between the terrestrial network (TN) and the non-terrestrial network that is under the control of the same core network, and the terminal could then connect either to a terrestrial base station or the gNB in the orbit. Spectrum sharing between satellite and terrestrial systems in a coexisting manner where the systems are separate (not under the same core) requires information exchange since spectrum sensing-based solutions cannot guarantee interference-free operations. Controlled sharing can be potentially enabled by database-assisted sharing where a third-party entity is giving rights to the lower priority sharing party with a given frequency and power allocation. For example, the licensed shared access (LSA) system studied in [23] has been implemented and shown to be able to control a scalable number of users and their resource allocations in such a way that interference at the primary user reception can be controlled. In the 3 GPP domain, the spectrum is divided into two frequency ranges (FRs), where FR1 covers frequencies below 6 GHz and FR2 covers those above 20 GHz. The S-band covering 1980-2010 MHz, and 2170-2200 MHz is identified by ITU for both TN and NTN components. Sharing is not feasible without appropriate interference mitigation techniques. In addition to frequency regulations, we have identified the following topics as very relevant for MLSS: (1) Space debris and the sustainable use of space are increasingly important due to the rapid increase in the number of satellites in space. (2) Territorial aspects and cross-border operations in the 3 GPP networks [21] must be developed in a way that regulations allow connecting and routing with core networks located in different countries than the user. (3) Ground station regulations must be clarified to support the increasing number of users from increasing ground locations while considering the current geopolitical situation. (4) Cybersecurity practices and guidelines are needed to ensure that MLSS systems remain secure.