# Adaptive Access Selection Algorithm for Large-Scale Satellite Networks Based on Dynamic Domain
## 3 DAA Algorithm Design
### Access Switching Mechanism
#### 3.2.1 Insufficient Satellite Resources  
To solve the problem of insufficient access satellite resources, the ES selects the backup access satellite \(\bar{\sigma}^{\prime}\) according to the prior knowledge obtained from the ACKs and the coverage time of the satellites. To obtain the state information of some satellites in the communication domain without the additional interactive information between the satellite and the Earth Station, the DAA algorithm does the following processing:  
1. When ES sends data packets to the access satellite, \([LON_{ES},LAT_{ES},D_{\max}]\) is added to the data packets;
2. After receiving the data packets sent by the ES, the access satellite forwards the data packets according to the routing table. After the satellite \(S_{n,m}^{L}\) in the set \(V^{\prime}\) receives the data packet, it decodes \([LON_{ES},LAT_{ES},D_{\max}]\) first, and then determines whether it is in the communication domain of the ES by Equation (3). If \(I_{n,m}^{con}>0\) in Equation (3), \(S_{n,m}^{L}\) is located in the communication domain of the ES. 3. If \(S_{n,m}^{L}\) is in the communication domain of the ES, \(\left[C_{L,n,m}^{t},\mathcal{E}_{t,n,m}^{t}\right]\) is added to the ACKs when \(S_{n,m}^{L}\) transmits ACKs. \(C_{L,n,m}^{t}\) represents the residual memory capacity of \(S_{n,m}^{L}\) at time \(t\), and \(\mathcal{E}_{L,n,m}^{t}\) represents the residual energy of \(S_{n,m}^{L}\) at time \(t\). 4. If \(S_{n,m}^{L}\) is not in the communication domain of the ES, \(S_{n,m}^{L}\) will delete \([LON_{ES},LAT_{ES},D_{\max}]\) before forwarding the data packet. \(S_{n,m}^{L}\) does not extra process the ACKs. Through the above steps, ES can obtain prior knowledge of the satellites in the set \(V^{\prime\prime}\). Set \(V^{\prime\prime}\) in some scenes includes multiple satellites. As shown in Figure 6, the set \(V^{\prime\prime}\) includes \(S_{2,2}^{L}\), \(S_{2,3}^{L}\) and \(S_{2,4}^{L}\) in addition to access satellite \(\bar{v}\). However, in some scenarios, set \(V^{\prime\prime}\) only includes access satellites \(\bar{v}\). As shown in Figure 7, set \(V^{\prime\prime}\) only includes \(\bar{v}\). Figure 6: The relationship between packet transmission path and communication domain Equation (1). For the scenario in Figure 6, the ES receives the memory capacity and energy remaining state of the satellites in \(\mathbf{V}^{\prime\prime}\) through ACKs. Calculate memory capacity and energy surplus rate according to the following Equations:  
\[U_{C}=\frac{C_{L,n,m}^{t}}{C_{L,n,m}},U_{\mathcal{E}}=\frac{\mathcal{E}_{L,n,m} ^{t}}{\mathcal{E}_{L,n,m}}, \tag{7}\]  
where \(C_{L,n,m}\) and \(\mathcal{E}_{L,n,m}\) represent the maximum memory capacity and the maximum energy value of \(S_{n,m}^{t}\), respectively. \(U_{C}^{T}\) and \(U_{\mathcal{E}}^{T}\) represent the residual memory and energy capacity thresholds, respectively. The ES first calculates the coverage time of the satellites in set \(\mathbf{V}^{\prime\prime}\) by Equation (3), then selects the satellite with \(U_{C}\), \(U_{\mathcal{E}}\) and coverage time satisfying the traffic volume requirements as backup access satellite \(\theta^{\prime}\). If there are multiple satellites in set \(\mathbf{V}^{\prime\prime}\) satisfying the condition of \(\tilde{\mathbf{v}}^{\prime}\), one of them is selected as the \(\tilde{\mathbf{v}}^{\prime}\) through Equation (6). When the current access satellite resources are insufficient, the ES chooses \(\tilde{\mathbf{v}}^{\prime}\) as the access satellite. Because \(\tilde{\mathbf{v}}^{\prime}\) is selected in the original path, no further routing is required after the ES switches to backup access satellite \(\tilde{\mathbf{v}}^{\prime}\). The choice of \(\tilde{\mathbf{v}}^{\prime}\) reduces the switching times and the consumption of resources by rerouting. For the scenario in Figure 7, only access satellite \(\tilde{\mathbf{v}}\) is in set \(\mathbf{V}^{\prime\prime}\).