# Towards Digital-Twin Assisted Software-Defined Quantum Satellite Networks
## 6 Conclusions  
Recently, there have been significant developments in different kinds of QDs, and several experiments employing single satellites have been conducted. Therefore, it is fundamental to deploy a specific QSB based on the principles of quantum entanglement and teleportation with the aim of connecting QCs on Earth to create a distributed quantum system with a computational capacity that goes far beyond the capabilities of any classical distributed computing system. The launch of a specific QSB will allow overcoming the limitations of OF links; therefore, also considering the technological advances in quantum satellite communications, we were motivated to conceive a system for the management  
Figure 11: Time required to obtain the entanglement on the paths generated during the entire simulation.  
Figure 12: Fidelity values obtainable on the satellite repeater chain.  
of a LEQ QSB. Taking into account the difficulties that are encountered in the creation of entanglement over long distances, a DT-assisted SDN QSB could be significant in making the process as efficient as possible, controlling the operations necessary to generate an E2E entanglement. In particular, we have conceived a dedicated architecture comprising a DT and an SDN Controller on the ground that controls the operations to configure the selected E2E paths. In addition, we have defined a dedicated protocol to configure the path based on the results provided by the DT to ensure efficient entanglement distribution on an E2E basis, optimizing, in particular, the monitoring procedure of the involved satellites performed by the DT. Specifically, we analyzed in terms of the attenuation, the links composing the E2E paths generated by the algorithm applied to the TG. Moreover, we evaluated the performance of the system by considering the time required to configure E2E paths, the time required to generate entangled states on an E2E basis, the RTT required to reach the satellites that compose the path, and the fidelity.  
The protocol has been evaluated at varying network conditions and thus the E2E paths, which are highly dependent on the variation of the satellite positions with respect to the GSs, thus evaluating the time required to configure the paths selected by the algorithm. From the performed simulations, it is possible to infer that the developed approach is efficient, considering that it guarantees as few as possible disconnections and the time required to reach the involved satellites is lower with respect to a system that does not include an optimization performed by a DT. Furthermore, the average entanglement rate achieved is significant, especially considering the potentially long connection recovery times, which are further impacted by the response time of the pointing mechanisms.  
Future development could consist of the research of new DT quantum satellite scenarios with the aim to improve the performance further also considering scenarios with a higher number of users.  
Conceptualization, R.P., F.C., T.P. and L.P.; methodology, R.P., F.C., T.P. and L.P.; software, R.P.; validation, R.P., F.C., T.P. and L.P.; formal analysis, R.P.; investigation, R.P., F.C., T.P. and L.P.; resources, F.C. and L.P.; data curation, R.P.; writing--original draft preparation, R.P., F.C., T.P. and L.P.; writing--review and editing, R.P., F.C., T.P. and L.P.; visualization, R.P.; supervision, F.C., T.P. and L.P.; and project administration, T.P. All authors have read and agreed to the published version of the manuscript.  
This work was partially supported by the European Union under the Italian National Recovery and Resilience Plan (NRRP) of NextGenerationEU, partnership on \"Telecommunications of the Future\" (PE0000001 - program \"RESTAT\").  
Not applicable.  
Data Availability Statement: Data is contained within the article.  
The authors declare no conflicts of interest.