# Handover Scheme in LEO Satellite Networks Based on QoE for Streaming Media Services
## 3 Simulation System Design for Handover and Access of Streaming
### Handover Scheme Design Based on Streaming Services  
To leave redundancy for handover failures, we set the handover to start when the data in the buffer are below the handover threshold \(H_{TInte}\). When the handover is about to take place, it is taken into account that the satellite environment is different from the terrestrial environment. The channel on the ground is almost unpredictable, so the strategy on the ground is to adopt the strategy of obtaining the maximum transmission rate possible and then filling the buffer [28]. In contrast, in satellite communication environments, satellite resources are limited while the channel is relatively stable and predictable. If the optimization is based on QoS indicators (such as bandwidth, delay, etc.) and does \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \(s_{1}\) & \(s_{2}\) & \(s_{3}\) & \(s_{4}\) & \(d_{1}\) & \(d_{2}\) \\ \hline \(-1.72\) & \(-0.04\) & \(-0.36\) & \(1.66\) & \(0.29\) & \(-3.29\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Values of the coefficients of Equations (3) and (4). not take into account the characteristics of streaming media services, then an excessive improvement of QoS may lead to communication performance overflow and a waste of satellite resources. In addition, multi-user contention for maximum bandwidth resources may also lead to a \"downward spiral effect\" [28]. Therefore, our access scheme is based on the QoE of streaming media. From Section 2.1, the channel capacity of the satellite to be linked by the user can be calculated for the entire service cycle with known power and satellite status. And from the analysis in the previous section, it can be seen that to ensure the user's QoE in streaming media playback, it is necessary to ensure that there is no rebuffering during the service. Therefore, the channel capacity during the user's access to the satellite needs to meet the following two conditions:  
* The average channel capacity from the time of access to the satellite until the satellite has flown to its highest elevation angle is not less than the bit rate required for the user's streaming service. * The buffer shall not be exhausted from the time of access to the satellite until the satellite reaches its highest elevation angle. Consider the first condition first. For the handover user, the elevation angle and trajectory of the currently accessible satellite are fixed, so the only parameters that the user can choose are the access power and which satellite. Suppose that the set \(S_{i}=\{S_{i,1},S_{i,2},...,S_{i,j},...\}\) is the set of all satellites within the access range of the user \(u_{i}\in\{u_{1},u_{2},...,u_{i},...\}\). In our paper, it is assumed that the total downlink power resource of each satellite in the system is \(P_{tot}\). Considering that the transmission rate of user services is guaranteed as much as possible, the range of selectable satellites is limited to the moments when the elevation angle is above \(10^{\circ}\) and is in elevation rise. For a satellite \(S_{i,j}\), its service time is \([\theta,t_{max}]\), where \(t_{max}\) is the length of time from when the satellite enters the service range to when the elevation angle is at its maximum [23]. A handover is initiated for user \(u_{i}\) at the time \(t_{acc}\) when the elevation angle of the satellite \(S_{i}\) relative to the user is \(\theta_{acc}\) (\(\theta_{acc}>10^{\circ}\)). Assuming that the power of the user's access to the satellite \(S_{i,j}\) is \(P_{i,j}\), the channel capacity variation brought into Equation (2) is  
\[C(t,P_{i,j})=B\text{log}_{2}(1+\frac{G_{tot}}{N}\cdot\frac{P_{i,j}}{L_{t}(t)}), \tag{6}\]  
where \(\theta_{acc}>\theta(t)>\theta_{max}\) and \(\theta_{max}\) is the maximum satellite elevation angle [23].