JUST360: Optimizing 360-Degree Video Streaming Systems With Joint Utility

360-degree videos, as a type of media that offers highly immersive experiences, often result in significant bandwidth waste due to incomplete views by users. This places a heavy demand on streaming systems to support high-bandwidth requirements. Recently, tile-based streaming systems combined with viewport prediction have become popular to improve bandwidth efficiency. However, since the viewport prediction is only reliable in the short term, maintaining a long buffer to avoid rebuffering is challenging. We propose JUST360, a joint utility based two-tier 360-degree video streaming system in this paper. To better improve the accuracy of utility evaluation, a utility model incorporates image quality and prediction accuracy is proposed to evaluate the contribution of each tile so that longer buffer and bandwidth efficiency can coexist. The optimal bitrate allocation strategy is determined by using model predictive control (MPC) to dynamically select the tiles according to their characteristics. Experiments show that our method successfully achieves higher PSNR and less rebuffering. Compared with other state-of-the-art methods, our proposed method can outperform the other methods by 3%-20% in terms of QoE.