# Multi-Layered Satellite Communications Systems for Ultra-High Availability and Resilience
## 2 Market Analysis and Regulations
### Regulatory Factors for MLSS Systems  
Regulations are needed to ensure that different systems can operate at their designated frequencies and to enable sustainable operations in the future. They provide an international framework to be followed by space nations--and ways to control and monitor the actual operations. In general, regulations cover many social, economic, and environmental topics such as territorial aspects, frequency management, and space safety. Regulations include spectrum regulation (International Telecommunications Union Radiocommunication Sector (ITU-R), regional, and country-specific regulations and authorities, licensing, and spectrum access rules), environmental regulations, and industrial standards. Spectrum regulations are needed to ensure the operations of planned MLSS systems, and these need to be defined first at the international level by ITU-R and later refined and implemented by regional and national administrations. The regulatory factors of MLSS spectrum use cover intersatellite links (ISLs), feeder links, and user links. Many topics were covered in the World Radio Conference 2023 (WRC-23) that was held in Dubai on 20 November-15 December 2023. For example, agenda item 1.17 was dedicated to determining \"appropriate regulatory actions for the provision of inter-satellite links in specific frequency bands, or portions thereof, by adding an inter-satellite service allocation where appropriate\". Suitable frequency bands and interference rules need to be determined for the links as well as for frequency sharing between GSO and NGSO satellite systems--and between satellite systems and terrestrial networks potentially coexisting in the bands where 5G NTN technology is used. Let us summarize the regulatory factors for each segment of the MLSS system. **Intersatellite links**: ISL links can be implemented either using radio frequency (RF) or optical technology. There are no standards defined for ISL links currently and no regulations for optical technology in space. Regarding the RF links, the ITU-R radio regulations [19] specify certain frequency bands for inter-satellite services as primary services: the K-band, the Ka-band, and the mm bands. Additionally, the footnotes of [19] indicate other bands allocated to other primary services that can also be used for the space-to-space direction, in the UHF, L-band, S-band, and C-band. Fixed-satellite service (FSS) connections also include, in some cases, satellite-to-satellite links, but this is not specified in the allocation tables. One solution is to use the bands allocated to industrial, scientific, and medical (ISM) applications [20]. The ISM band that corresponds to a fixed-satellite service is the 5.725-5.875 GHz. **Feeder links** are categorized as FSS links. The footnotes in Article 5 of [19] indicate for which kind of services the FSS can be used in each frequency band, whether the FSS link is for GSO or NGSO satellites, and whether the link can be used as a feeder link to broadcasting (BSS), mobile (MSS), or fixed satellite systems. Hence, deciding which band is appropriate requires knowing the satellite's orbit and the service that the satellite is providing to the users of that service. Article 22 in [19] includes Equivalent Power Flux Density (EPFD) limits radiated by space stations and Earth stations of NGSO systems in FSS in certain frequency bands. **User links**: Depending on the scenario, those links can be MSS, FSS, BSS, or Earth Exploration Satellite Service (EESS). It is more important to check the most appropriate standards for those links than the ITU-R regulations. They specify all the requirements both ends of the system must comply with. For example, the 3 GPP has guidelines for extraterritorial 5G systems [21]. **GSO-NGSO coexistence in the same band**: To minimize the terminal costs, a solution in which the terminal can be connected to both GSO and NGSO would be necessary.