都市型車載隨意網路之可靠視訊串流機制

Abstract

在車載網路(VANET)上傳遞視訊串流是近幾年來熱門興起的研究議題，它能提供乘客更安全的行車環境及娛樂服務。但由於隨意網路中拓樸快速改變的特性，如何在車載網路的環境中提供穩定的車輛間資料傳輸路徑便成了一個很大的挑戰。也由於車載網路中的車輛使用無線網路作為傳輸媒介互相傳遞資料，而無線傳輸易於出現錯誤的特性，使得資料在多次傳輸的過程之中遺失，造成了接收端收到的影像畫質下降。在本篇論文中，我們提出了都市型車載隨意網路之可靠視訊串流機制(RVS)，它結合了車輛移動相似度及彈性巨方塊順序。我們使用容錯的機制來復原在傳輸過程中遺失的資料，藉以提升接收端的影像畫質，並且找出較為穩定的資料傳輸路徑，使車輛間資料傳輸更為可靠。資料傳輸路徑是由路段所組成而不是由車輛所組成，這樣可以減少路徑斷裂並且提升路徑的可靠度。彈性巨方塊順序將影像編碼成為多個片組，而每個片組是由許多巨方塊所組成，以提供接收端影像容錯的能力。藉著車輛移動相似度可以選擇較穩定的相鄰車輛作為傳遞中繼點，可使車輛間資料傳輸更為可靠。為了評估本篇論文所提出的方法，我們比較了F-AODV ，它結合了彈性巨方塊順序及AODV的方法，而所比較的參數是封包傳輸率以及峰值信噪比。模擬的結果顯示，在都市環境下，與F-AODV 相比，我們提出的方法提升了 7% 的封包傳輸率及1.3 dB的峰值信噪比。

In recent years, video streaming in the vehicular ad hoc network (VANET) has become a popular research issue. Because of the rapid changing network topology, maintaining stable paths to support inter-vehicle video streaming transmissions is a great challenge in VANETs. Due to the error-prone characteristic of wireless communication, routing packets over multiple hops results in packet loss and causes reconstructed video of poor quality at the receiver. In this thesis, we propose a road-based resilient video streaming (RVS) scheme that integrates flexible macroblock ordering (FMO) and vehicle moving similarity. We intend to enhance video streaming quality at the receiver by recovering lost packets with error resilience and choose more stable routing paths to make inter-vehicle data transmissions more reliable. In our scheme, routing paths consisting of road blocks rather than vehicular nodes can reduce broken links to enhance route stability. FMO encodes images into slice groups consisting of macroblocks to provide error resilience at the receiver. Based on vehicle moving similarity our scheme selects more stable neighbors as relay nodes to make inter-vehicle transmissions more reliable. To evaluate the performance of the proposed RVS, we compare it with a classical ad hoc protocol, F-AODV, which combines FMO and AODV, in terms of delivery ratio and peak signal-to-noise ratio (PSNR). Simulation results under urban settings show that the proposed RVS improves the delivery ratio by 7% and the received video stream quality (in terms of PSNR) by 1.3 dB compared with F-AODV.