# Load-Balancing Routing for LEO Satellite Network with Distributed Hops-Based Back-Pressure Strategy
## 6 Simulation Performance and Analysis  
### Simulation Setup  
The performance of the DHBP routing strategy is evaluated on a giant inclined orbit constellation on the OMNET++-based network simulation platform. The constellation consists of 648 satellites with a total of 18 orbits. In each orbit, 36 satellites are evenly distributed. The orbit has an altitude of 550 km and an inclination of 53\({}^{\circ}\). In terms of network parameter settings [41], we set up four two-way ISLs for each satellite (two inter-plane ISLs and two intra-plane ISLs). The link transmission rates of uplink, downlink, and ISLs are set to 10 Mbps [42]. A constant flow with the constant packet size (512 Byte) is adopted. The time for each round of simulation is set to 100 seconds. The orbital parameters and network parameters are shown in Table 2.  
Due to the uneven geographical distribution of global communication load, eight source and destination nodes are set up, which are combined into eight groups of source-destination pairs. The distribution of satellites and traffic nodes is shown in Figure 8. Table 3 lists satellite network traffic pairs. The network traffic is sent from the ground station near the source satellite and is connected to the LSN leveraging the closest satellites. Traffic is transmitted down to the terrestrial network upon reaching the satellite nearest to the destination.  
We compare DHBP with distance-based back-pressure routing (DBPR) [4], which uses link distance rather than hops count as the backlog metric of back-pressure routing. In order to ensure the accuracy of the comparison, the permitted transmission region of DHBP and DBPR is limited in a rectangular area. The second comparison routing protocol is open shortest path first (OSPF) [43], which utilizes [PERSON]'s shortest path. The third comparison routing protocol is state-aware and load-balanced routing (SALB) [8]. SALB determines routing paths distributively, and dynamically adjusts the queue delay weight based on link states. The following performance metrics are adopted to comprehensively measure the performance of routing protocols.  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **Parameter** & **Value** \\ \hline \multirow{4}{*}{Orbital parameters} & Orbit height (km) & 550 \\  & Number of satellites & 648 \\  & Number of orbital planes & 18 \\  & Number of satellites per plane & 36 \\  & Orbital inclination (\({}^{\circ}\)) & 53 \\ \hline \multirow{4}{*}{Network parameters} & Buffer queue size & 100 \\  & Minimum elevation of gateway (\({}^{\circ}\)) & 30 \\ \cline{1-1}  & Uplink/downlink rate (Mbps) & 10 \\ \cline{1-1}  & Inter-satellite link rate (Mbps) & 10 \\ \cline{1-1}  & Packet size (byte) & 512 \\ \hline \hline \end{tabular}
\end{table}
Table 2: System parameters.  
Figure 8: Distribution of LEO satellite constellation and ground nodes.  
* Average delay. Average time of transmitting packets from source to destination;
* Average number of forwarding per packets. The average number of times each packet is forwarded from source to destination, which measures the average delivery cost;
* Throughput. Overall, the successful delivery rate of the packet to the destination node;
* Data delivery ratio. The ratio of messages successfully delivered to the destination satellites to all messages sent by source satellites in the network.