# Multi-Layered Satellite Communications Systems for Ultra-High Availability and Resilience
## 7 Conclusions  
This article summarizes technical and economic studies related to multi-layered satellite systems that may consist of GSO and NGSO satellites working together to provide ultra-reliable connections with high availability. This document covers market analysis and potential use cases, technical enablers, and regulations detailing the status and required developments to make visualized systems a reality. The developed MLSS concept and architecture define the building blocks, the connectivity links, and their frequencies. The results from system modeling and simulations show that the depicted concept can increase the resilience and availability of connections to the people and machines in remote areas. We implemented the testbed that emulates the channel according to MLSS simulations and measured the achievable performance considering 5G backhauling. The results show that MLSS backhauling requires the use of buffering to cope with a large amount of jitter over NGSO links. In practice, the delay over the GEO link can be considered only three times larger than the delay over the NGSO link in the case of reliable and deterministic communication. There are still many technical topics that need to be covered to reach tightly integrated MLSS systems providing reliable internet connections from orbit. Therefore, multiple recommendations for future work are given.  
Conceptualization, M.H. and A.A.; methodology M.H.; market analysis, M.V.; technology analysis, A.A. and L.L.; regulatory analysis, M.H.; simulation software, M.M., A.Y.-C. and H.Z.; writing the manuscript, M.H., A.A., M.M., A.Y.-C., M.V., L.L. and M.C.; architecture visualizations, M.V. and L.L.; experiments and analysis of results, M.M., A.Y.-C., M.C. and H.Z. All authors have read and agreed to the published version of the manuscript.  
This research was carried out in the framework of the Multi-Layered SATCOM Systems project, under a program funded by the European Space Agency (ESA), grant number 4000137517/22/NL/FGL. The work was also supported by the 6G-SatMTC project that is funded by Business Finland. The views presented in this paper are those of the authors and do not necessarily reflect the official view of the European Space Agency or Business Finland. The APC was covered by the APC waiver.  
The original contributions presented in the study are included in the article. Additional data sharing including the used software is not possible since they are part of an ongoing study.  
The authors would like to acknowledge [PERSON], [PERSON], [PERSON], and [PERSON]. Their contributions during the work have been valuable.  
Authors [PERSON], [PERSON], [PERSON] and [PERSON] were employed by the company VTT Technical Research Centre of Finland Ltd. Authors [PERSON] and [PERSON] were employed by the company Inmarsat. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.