## 4 Problem Equation
### A3C Algorithm
(4) Unified consideration of LEO satellite elevation state, communication link state, GEO data relay satellite transmission state, and computing state, regardless of caching state, expressed as A3C-based without caching scheme. (5) Unified consideration of LEO satellite elevation state, communication link state, GEO data relay satellite transmission state, and caching state, regardless of computing state, expressed as A3C-based without computing scheme. (6) Direct allocation of resources under static network conditions, expressed as A3C-based no scheme [40]. ### Simulation Result

The simulation results in this paper are discussed below. Figure 6 shows the convergence performance under different schemes. From the simulation, we can see that, at the beginning of deep reinforcement learning, the expected benefit per unit resource is low. With the increase of training times, the expected benefit of unit resources tends to be stable. The proposed A3C-based all scheme takes into account the coverage area of the LEO satellite, the communication link state between users and the LEO satellite, the transmission state of the GEO data relay satellite, the caching state of caches, and the computing state of the MEC server, which has better resource utilization efficiency. Figure 7 shows that with the increase in elevation angles of users and LEO satellites, the expected benefits per unit resource of the SIN increase gradually. The proposed A3C-based all scheme takes into account the coverage area of the LEO satellite, the communication link state between users and the \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Values** & **Descriptions** \\ \hline \(B_{u}^{l}\) & 6 MHz & Bandwidth allocated by LEO satellite \(l\) to user \(u\) \\ \(B_{l}^{lg}\) & 6 MHz & Bandwidth allocated by GEO satellite \(lg\) to user \(l\) \\ \(\delta_{l}\) & 2 units/MHz & Payment price using LEO spectrum resources \\ \(\delta_{lg}\) & 2 units/MHz & Payment price using GEO spectrum resources \\ \(\varsigma_{c}\) & 4 units/Mbits & Payment price using caching resources \\ \(\eta_{m}\) & 1 unit/J & Payment price using computing resources \\ \(\tau_{u}\) & 15 units/Mbps & The unit transmission fee charged to the user \\ \(\kappa_{u}\) & 10 units/Mbps & The unit caching fee charged to the user \\ \(\phi_{u}\) & 5 units/Mbps & The unit computing fee charged to the user \\ \(\theta_{u,\max}^{l}\) & \(\pi/2\) & Maximum elevation between user u and satellite \(l\) \\ \(n_{u}\) & 6 Mcycles & Number of cycles a CPU takes to complete each space task \\ \(e_{m}\) & 1 J & The energy consumed by the CPU in one lap \\ \(o_{u}\) & 3 Mbits & Task content \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulation parameter setting. LEO—low Earth orbit; GEO—geostationary orbit; CPU—central processing unit. LEO satellite, the transmission state of the GEO data relay satellite, the caching state of caches, and the computing state of the MEC server, which has better resource utilization efficiency. Figure 8 shows that, with the increase of the task content, the cost of caching charged to users increases gradually; thus, the expected benefit of unit resources of the SIN decreases gradually. The proposed A3C-based all scheme takes into account the coverage area of the LEO satellite, the communication link state between users and the LEO satellite, the transmission state of the GEO data relay satellite, the caching state of caches, and the computing state of the MEC server, which can achieve better expected benefits per unit resource. Figure 9 shows the relationship between the unit charging price for using transmission resources and the expected benefit of the unit resource. With the increase of the unit charging price for using transmission resources, the expected benefit of the unit resource of the SIN increases gradually. Figure 8: Expected benefits of unit resources under different task content. Figure 6: Convergence performance under different schemes. Figure 7: Expected benefits of unit resources under different elevation angles.