# Optical Wireless Fronthaul-Enhanced High-Throughput FC-AE-1553 Space Networks
## 5 Simulations, Results, and Discussions
### Factors for HSN Bandwidth
#### 5.5.2 Results and Discussion  
As depicted in Figure 14, the inclusion of wireless Li-Fi in the original FC-AE-1553 network resulted in remarkable improvements in both throughput and bandwidth. When the number of wireless links increased, there was a corresponding increase in the bandwidth. In the theoretical analysis, the upper bandwidth of the existing FC-AE-1553 space network is determined by the FC's physical link rate and the topology of the system. \(B_{hybrid}\) denotes the hybrid system's total bandwidth, \(N_{backbone}\) denotes the number of backbone networks, and \(\eta_{code}\) denotes the coding efficiency. \(N_{wireless-link}\) denotes the number of wireless links, \(R_{fc}\) denotes the FC's physical link rate, and \(R_{lifi}\) denotes the Li-Fi's physical link rate. The theoretical upper bandwidth limit equation is a summary of all link rates. \(x\) denotes the number of wireless links, and \(\eta_{loss,x}\) denotes the loss rate of the Li-Fi channel. \[B_{hybrid}=N_{backbone}\times R_{fc}\times\eta_{code}+\sum_{x=1}^{N_{ wireless-link}}(1-\eta_{loss,x})\times R_{lifi} \tag{36}\]  
The increased bandwidth of 48 Gbps was smaller than the Li-Fi link rate of 10 Gbps when the number of added wireless links was 18. The hybrid network's bandwidth in the simulated system was observed to be lower than the theoretical value due to multiple factors. Firstly, the environment-dependent packet loss introduced in wireless Li-Fi communication contributed to the reduction in bandwidth. Secondly, the time-slice-based traffic scheduling algorithm incurred certain overheads, making it challenging to fully utilize all available network time slices, further impacting the overall bandwidth. Additionally, another significant reason for the deviation from the theoretical value was the incomplete filling of the network caused by randomly generated services that did not fully occupy their capacities. These combined factors resulted in the observed discrepancy between the actual and theoretical network bandwidths in the simulated system. The network bandwidth was not only affected by the number of wireless links but also by the size of the small cycle. A larger small cycle led to a lower total bandwidth. Within a certain range, the impact of the small cycle on the bandwidth was minimal, whereas the number of wireless links had a relatively greater influence. As shown in Figure 15, when the transmission flow was within a smaller range, smaller small cycles resulted in higher bandwidth. However, when the transmission flow was within a larger range, the impact of the small cycle on the bandwidth was not significant. Therefore, in the network, to achieve more effective bandwidth, the value of the small cycle needs to match the current transmission's throughput capacity. Small cycles can be set larger for high-throughput transmissions and smaller for low-throughput transmissions. The practical effective bandwidth was calculated using (37). It is obtained by computing the total throughput within a small period, where the total throughput is the accumulation of transmissions from both the FC and the Li-Fi channel. \[ \begin{split} B_{eff}&=\frac{total\ Throughput}{ Cycle\ Period}=\frac{\sum_{i=1}^{total\ node}\ Throughput\ of\ node\ i}{Cycle\ Period}\\ &=\frac{\sum_{i=1}^{total\ node}\left(W(fc,i)\right)+W(lifi,i) \right)}{Cycle\ Period}\end{split}  \tag{37}\]  
In the equation, \(W(fc,i)\) denotes the FC traffic throughput of node \(i\), and \(W(lifi,i)\) denotes the Li-Fi traffic throughput of node \(i\). The actual throughput is derived from the effective time-slot time, after removing the protocol overhead, multiplied by the link rate. Subsequently, we compared this result with the traffic requirements, selecting the smaller of the two as the actual throughput capacity. The primary difference between the FC traffic and Li-Fi traffic hinges on their service frequencies. The FC traffic can only be served once, whereas the Li-Fi traffic has the capacity to be served multiple times.