以可適性媒體播放技術改善垂直換手過程之視訊品質研究

Abstract

近來，有越來越多的人透過智慧型行動裝置來使用視訊串流服務，包括隨選視訊以及視訊會議等。由於這些行動裝置通常支援雙模甚至多模網路介面，因此在使用視訊串流服務的同時，有可能會因為網路品質的變化而需要進行異質網路間的垂直換手，以切換至最佳的網路介面。在這樣的換手過程中，封包群體遺失或是延遲送達的現象會較傳統因無線通道下造成的問題來的嚴重，而使得視訊串流的品質大幅的下降。雖然相關文獻曾提出以「播放快取監視機制」和「接收速率監視機制」來做為控制播放速率的方式，但這些機制並不能有效解決在異質網路垂直換手過程中所遇到的問題。 有鑑於此，在本論文我們利用「可適性媒體播放」的技術，小幅度降低播放的速率來增加可播放畫面的比率，以改善封包少量、間歇性的遺失或是延遲之下的視訊品質。我們首先針對異質網路換手的特性，進行「換手時機」以及「換手期間」的預測，以獲得離換手所剩餘的時間和換手所需的時間。其次，我們將這些資訊跨層提供給「可適性媒體播放」模組，利用排程規劃執行該技術的時機和期間，並且設計不同的演算法來處理使用者的移動行為。我們使用NS-2來做為驗證可適性媒體播放技術的模擬平台，從模擬結果中可以發現，我們提出的技術可以有效的改善異質網路換手對視訊串流品質造成的影響。

Recently, there are more and more people using video streaming services through intelligent mobile devices, including on-demand video and video conference. Since these mobile devices often support the dual-mode or multi-mode network interfaces, it will switch to the best quality network while doing video streaming services by vertical handover. In the handover process, the burst packet loss or delay delivery will be more serious than the same events happened in ordinary wireless channels, and it will reduce the video quality obviously. Although the literature has proposed the “playout buffer monitoring mechanism” and “arrival rate monitoring mechanism” to control playout rate, they cannot effectively solve the problems occurred during vertical handover. According to this, we use 'adaptive media playout' technology in this thesis. By slightly decreasing playout rate, it could increase the proportion of playable frame to improve the video quality in small, intermittent packet loss and delay network condition. Firstly, we refer the characteristic of vertical handover to predict “handover time” and “handover duration”, to obtain the handover remaining time and the handover spending time. Secondly, we provide above cross-layer information to “adaptive media playout”, then using the schedule to plan the technology execution time and duration. We also design different algorithms to handle the user mobility. We use NS-2 to be the simulation platform to verify the proposed adaptive media playout technology. From the simulation results, we could find out that the proposed technique can effectively improve the impact of the video streaming quality on heterogeneous network handover.