# Handover Scheme in LEO Satellite Networks Based on QoE for Streaming Media Services
## 3 Simulation System Design for Handover and Access of Streaming  
In this section, we design the access and handover algorithm for the QoE indicators of on-demand streaming media service in the subscriber communication service, and we simulate the entire service process to check the QoE performance of the proposed algorithm. Figure 3 is the algorithm structure diagram of the simulation we have built, which consists of four parts representing the four states of the user, which are idle (represented by state 0), playback (represented by state 1), initial buffering (represented by state 2), and rebuffering (represented by state 3). The green box shows the two algorithm modules for accessing and handover designed in this paper. The simulation process is divided into multiple time slots, and each time slot performs the simulation process once for each user. * The user in an idle state is in the gap between streaming media playback, and the user may pause the playback service for a period of time because he/she is looking for a new video of interest before ordering a new streaming media. When the idle time is over, the user is handed over to the initial buffering state. * The user is in the playback state when the service is being used. The satellite downlink transmits streaming packets from the satellite to the buffer at the user's terminal, while the user plays the streaming files in the buffer in chronological order. This state will determine whether the user's service is stalled, whether the buffer is overflowing, and whether the playback is complete and other conditions so as to change the user's state. When the streaming data in the buffer of the user terminal are below the handover threshold \(H_{Titne}\) and at the same time, the satellite elevation angle is decreasing, the system starts trying to handover. If none of the candidate handover satellites satisfy the condition, then the current time slot is abandoned for handover, and the handover will wait for the next time slot. When the satellite handover fails several times, and the buffer is below the power occupation threshold \(H_{oc}\), it begins to enter the occupancy handover. The occupancy handover takes up a portion of the other user's power, allowing the current user to meet the minimum power requirement. * The user in the initial buffering state is in the initial buffering phase after having just ordered a streaming service. The user will not play the video at this stage. First, the system will determine whether a suitable satellite has been selected. If not, it will enter the satellite access module. Then, the system sends the streaming media packet to the buffer. When the data in the buffer exceed the playback threshold, it transfers to the playback state. * The user in the rebuffering buffer state is switched to this state after the buffer is exhausted in the playback state. In this state, the user stops playback and starts buffering until the buffer fills up to the playback threshold. Finally, it will detect if a handover is needed, usually after repeated failed handovers lead to buffer exhaustion,which then causes playback to stop. At this point, the system will attempt to handover at each time slot until playback resumes. In this paper, we design the QoE-based handover and access scheme for streaming services, so we must first consider how the QoE of streaming services is evaluated. For the evaluation of QoE in this type of service, there are existing papers using their own evaluation methods [19]. Given that a QoE assessment is highly subjective, this paper therefore refers to the ITU-T P.1201 assessment model [24], which is capable of estimating the quality of Progressive Download (PD) streaming applications; i.e., it is used for the quality prediction of non-adaptive TCP-based streams. The model predicts the Mean Opinion Score (MOS) [25] on a 5-point Absolute Category Rating (ACR) scale as the global multimedia MOS. This scheme to measure the QoE of streaming media is often used in multimedia research [26].