利用自然、相对平滑和转码多播机会实现多质量360 VR视频的最佳无线流传输
Optimal Wireless Streaming of Multi-Quality 360 VR Video by Exploiting Natural, Relative Smoothness-enabled and Transcoding-enabled Multicast Opportunities
摘要：
在本文中，我们想研究多质量平铺360虚拟现实（VR）视频从服务器到多个用户的最佳无线流。为此，我们建议最大限度地利用潜在的组播机会，有效地利用多质量平铺360 VR视频和计算资源的特点在用户端。特别地，我们考虑在一个视场（FoV）中的质量变化的两个要求，即，绝对平滑度要求和相对平滑度要求，以及两种视频回放模式，即，直接回放模式（没有用户代码转换）和代码转换回放模式（有用户代码转换）。除了自然的多播机会，我们引入了两种新类型的多播机会，即，相对平滑使能的多播机会，它允许灵活的观看质量和通信资源消耗之间的权衡，和转码使能的多播机会，它允许灵活的计算和通信资源消耗之间的权衡。然后，我们建立了一个新的数学模型，反映了自然的，相对平滑使能和转码使能的组播机会的平均传输能量和转码能量的影响。基于该模型，在对质量变化和视频播放模式有不同要求的四种情况下，分别对传输资源分配、播放质量等级选择和传输质量等级选择进行优化，使能耗最小。通过比较四种情况下的最优值，我们证明了当可以利用更多的多播机会时，能量消耗减少。最后，数值结果表明，所提出的解决方案比现有的计划有很大的收益，并证明了有效利用这三种类型的组播机会的重要性。
英文摘要：
In this paper, we would like to investigate optimal wireless streaming of a multi-quality tiled 360 virtual reality (VR) video from a server to multiple users. To this end, we propose to maximally exploit potential multicast opportunities by effectively utilizing characteristics of multi-quality tiled 360 VR videos and computation resources at the users' side. In particular, we consider two requirements for quality variation in one field-of-view (FoV), i.e., the absolute smoothness requirement and the relative smoothness requirement, and two video playback modes, i.e., the direct-playback mode (without user transcoding) and transcode-playback mode (with user transcoding). Besides natural multicast opportunities, we introduce two new types of multicast opportunities, namely, relative smoothness-enabled multicast opportunities, which allow flexible tradeoff between viewing quality and communications resource consumption, and transcoding-enabled multicast opportunities, which allow flexible tradeoff between computation and communications resource consumptions. Then, we establish a novel mathematical model that reflects the impacts of natural, relative smoothness-enabled and transcoding-enabled multicast opportunities on the average transmission energy and transcoding energy. Based on this model, we optimize the transmission resource allocation, playback quality level selection and transmission quality level selection to minimize the energy consumption in the four cases with different requirements for quality variation and video playback modes. By comparing the optimal values in the four cases, we prove that the energy consumption reduces when more multicast opportunities can be utilized. Finally, numerical results show substantial gains of the proposed solutions over existing schemes, and demonstrate the importance of effective exploitation of the three types of multicast opportunities.
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