# Optical Wireless Fronthaul-Enhanced High-Throughput FC-AE-1553 Space Networks
## 5 Simulations, Results, and Discussions
### Performance Comparison between the HSN and FC-AE-1553
#### 5.2.2 Results and Discussion  
Figure 12 shows a comparison of the throughput, bandwidth, channel selection, and delay between the original FC network and the network with wireless enhancement. Blue represents the existing FC-AE-1553 space system, green represents the hybrid FC and Li-Fi space network, dark orange represents the scenario of FC within the HSN, and light orange represents the scenario of the Li-Fi channel within the HSN. Figure 11: HSN simulation topology. \begin{table}
\begin{tabular}{c c} \hline \hline
**FC Topology Parameters** & **Value/Rule** \\ \hline Number of backbone networks & 1 \\ NC number of backbone networks & 1 \\ NT number of backbone networks & \textgreater{}2 \\ Connections of backbone network nodes & Linked directly with each other; Total Number: n(n \(-\)1)/2 1 \\ Number of access networks & 2 \\ NC number of backbone networks & 1 \\ NT number of backbone networks & \textless{} 1 \\ Connections of access network nodes & NT linked with its NC node; Total Number: m \\ Connection between backbone and access network & Network Gate: Both NT of backbone and NC \\ \hline
**Li-Fi Topology Parameters** & **Value/Rule** \\ \hline Hybrid node number & \textgreater{}4 \\ Connection number & \textgreater{}Hyrbrid node number \\ Distance & Random (no larger than 10 m) \\ \hline
**Transmission Parameters** & **Value/Rule** \\ \hline FC physical-layer link rate & 4.25 Gbps (8B/10B encoding and decoding) \\ Li-Fi physical-layer link rate & 10 Gbps \\ \hline \hline \end{tabular} \({}^{1}\) n denotes the total number of backbone network.  
\end{table} 
Table 3: Simulation metrics. After the wireless enhancement, the throughput and bandwidth increased by a factor of 20.5, the network transmission frequency expanded by a factor of 9, and the average delay was reduced to 87.3% of the original value. The minimum delay was 46.3% of the original, and the maximum delay remained unchanged (because the maximum delay is determined by the longest FC path in the network, whether it is a pure FC network or a hybrid network). With respect to the reduction in the average latency, the latency of Li-Fi, operating at a higher rate of 10 Gbps, was approximately 34% of the latency of FC (compared to the effective rate of FC, which is approximately 3.4 Gbps). This translates into a significant reduction of 66%, surpassing our initial expectations. Additionally, apart from the rate factor, when FC tasks involved multi-hop link selection, each task incurred an additional waiting delay. In contrast, by opting for the Li-Fi channel for transmission, these tasks eliminated the need for such a waiting delay. Since the waiting delay significantly out-weighed the transmission delay, selecting more Li-Fi channels for services that span across access networks resulted in a remarkable reduction in the average latency. Thus, achieving a reduction of 87.3% aligns perfectly with our anticipated outcomes. By comparing the third and fourth bars of each subplot in Figure 12, we can clearly see that the increases in the network throughput and bandwidth in the hybrid network were mainly caused by the newly added Li-Fi channel. When observing the third graph in the first row, we can see that the number of services in the hybrid network increased, and these additional services mainly came from the Li-Fi channel. Compared to the FC, more services were preferred in the Li-Fi channel for three main reasons: first, Li-Fi has a higher network bandwidth; second, Li-Fi can provide shorter paths, thus reducing latency; finally, Li-Fi's time slots can offload services multiple times within a small cycle. The minimum latency in the hybrid network significantly decreased. In the fourth bar, we can see that the lowest latency came from the Li-Fi network thanks to its high bandwidth and short path advantages. However, the maximum latency did not change, mainly because this part of the delay was still caused by the multi-hop services of the FC network.