# Multi-Layered Satellite Communications Systems for Ultra-High Availability and Resilience
## 5 Results: Findings from Simulations and Testbed Activities  
### Simulation Studies  
To study the defined system, we implemented a simplified version of it with our simulation software, called SCNE [46]. The modeled MLSS system was defined with the parameters presented in Table 2. As depicted in Figure 5, SCNE consists of a Systems Tool Kit (STK) and ns-3 simulators, and an orchestrator between these elements. STK is used for modeling the satellite constellation part, i.e., satellite, gateway, and user terminal locations, and the visibility and link budgets between all nodes. This information is then used in the ns-3 network simulator to create a similar scenario with the physical layer (L1) based on the link characteristics computed in the STK. The upper layers (from L2 to applications) are modeled solely inside ns-3. The role of the orchestrator is to collect and compute all the necessary information from the STK scenario into configuration files that are then read by the ns-3. Figure 5: SCNE high-level architecture [45]. The target of the simulation studies was to see whether there are benefits to the use of the MLSS system vs. a single-layer system. Our hypothesis was that the MLSS can support both delay and jitter (as standard deviation from the mean delay) sensitive traffic depending on via which satellite layer the packets are routed, while a single-layer system can support only one of those elements, depending on the orbit. The key performance indicators (KPIs) selected for the performance assessment were end-to-end delay, jitter, packet loss, and throughput. The simulation results (end-to-end delay) also served as \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Value** & **Notes** \\ \hline LEO altitude & 1000 km & \\ \hline LEO inclination & 90 deg & Polar orbit \\ \hline Number of LEO satellites & 60 & Six planes, 10 satellites each \\ \hline LEO-LEO ISL & 4 & Two intra-plane (North, South), two inter-plane (East, West) \\ \hline LEO-GEO ISL & 6 & one per each LEO plane \\ \hline ISL frequency & 23.55 GHz UL, 22.55 GHz DL & K-band \\ \hline ISL tx power & 15 dBW 1 & LEO-LEO, parabolic antenna \\  & 20 dBW 1 & LEO-GEO, parabolic antenna \\ \hline LEO-LEO ISL On/Off & 65 deg latitude & Inter-plane ISLs off in polar areas \\ \hline LEO user link frequency & 28.6 GHz UL & Ka-band \\  & 18.8–19.28 GHz DL & 31 beams \\  & Satellite covers an area with diameter of 4819 km \\ \hline LEO user link tx power & 15 dBW 1 & ITU-R S.1528 circular antenna \\ \hline LEO feeder link frequency & 29.1 GHz UL, 19.3 GHz DL & Ka-band \\ \hline LEO feeder link tx power & 15 dBW & ITU-R S.1528 circular antenna \\ \hline Number of GEO satellites & 3 & \\ \hline GEO-GEO ISL & 2 & To other two GEO satellites \\ \hline GEO-GEO ISL frequency & 193 THz & Optical link \\ \hline GEO-GEO ISL tx power & 10 dBW & Gaussian optical antenna, gain 100 dB \\ \hline GEO user link frequency & 1525 MHz DL & L-band, 201 beams, satellite covers an area with \\  & 1620 MHz UL & diameter of 16,182 km \\ \hline GEO user link tx power & 20 dBW & ITU-R S.672-4 circular antenna \\ \hline GEO feeder link frequency & 1610 MHz UL & L-band \\  & 1613.8 MHz DL & L-band \\ \hline GEO feeder link tx power & 20 dBW & ITU-R S.672-4 circular antenna \\ \hline Number of UTs & 51 & Random and fixed locations \\ \hline UT tx power & 8 dBW/ & Ka-band/L-band, \\  & 10 dBW & ITU-R S.465-5 antenna \\ \hline Number of GWs & 3 & Goldstone (USA), Esrange (SWE), Kaena (USA) \\ \hline GW tx power & 15 dBW & Ka- and L-band, \\  & & ITU-R S.465-5 antenna \\ \hline Min elevation angle & 8 deg & For both UT and GW \\ \hline User datagram protocol (UDP) & 1400 bytes/packet & Between random UT-GW pairs \\ traffic flows & 10 s packet interval & \\ \hline Simulation duration & 24 h & \\ \hline \hline \end{tabular}  
* Tx powers do not include antenna gain.  
\end{table} 
Table 2: Space segment configuration. inputs to the testbed activities that are described in Section 5.2.