The problem addressed is that of optimally controlling, in a decentralized fashion, the download of mobile video, which is expected to comprise 75 % of total mobile data traffic by 2020. The server can dynamically choose which packets to download to clients, from among several packets which encode their videos at different resolutions, as well as the power levels of their transmissions. This allows it to control packet delivery probabilities, and thereby, for example, avert imminent video outages at clients. It must however respect the access point's constraints on bandwidth and average transmission power. The goal is to maximize video "Quality of Experience" (QoE), which depends on several factors such as (i) outage duration when the video playback buffer is empty, (ii) number of outage periods, (iii) how many frames downloaded are of lower resolution, (iv) temporal variations in resolution, etc.
It is shown that there exists an optimal decentralized solution where the AP announces the price of energy, and each client distributedly and dynamically maximizes its own QoE subject to the cost of energy. A distributed iterative algorithm to solve for optimal decentralized policy is also presented. Further, for the client-level QoE optimization, the optimal choice of video-resolution and power-level of packet transmissions has a simple monotonicity and threshold structure vis-a-vis video playback buffer level. When the number of orthogonal channels is less than the number of clients, there is an index policy for prioritizing packet transmissions. When the AP has to simply choose which clients' packets to transmit, the index policy is asymptotically optimal as the number of channels is scaled up with clients.
Coalition Game-based Approach for Improving the QoE of DASH-based Streaming in Multi-servers Scheme
HTTP动态自适应流媒体(Dynamic Adaptive Streaming over HTTP,DASH)正在成为大规模有效视频流量交付的事实方法,其首要成功因素是赋予流媒体客户端完全的自主权,使其更加智能,并在基于拉取的范式下实现粒度视频块的分散式视频质量决策逻辑。然而,客户端的纯粹自主性本质上导致了整体自私的环境,其中每个客户端独立地努力提高其体验质量(QoE)。因此,客户端会伤害对方,包括自己,由于他们的感知范围有限。这个缺点可以通过采用一种机制,具有全局视图,从而可以有效地管理可用资源来解决。在本文中,我们提出了一个基于博弈论的方法来解决多服务器设置中的客户端的自私问题,而不影响其自治。特别地,我们采用联盟博弈框架来影响客户端到最好的服务器,最终最大限度地提高客户端的整体平均质量,同时防止重新缓冲。我们通过大量的实验验证了我们的解决方案,并展示了所提出的解决方案的有效性。