- 學位論文
用於車間通訊的高效能交通訊息傳送與影像廣播之解決方案設計
On the Design of Highly Efficient Traffic Information Forwarding and Video Broadcasting Solutions for Inter-Vehicle Communication
摘要
對於高速公路上之車間通訊應用而言，若能有效率地傳送適當及有用的交通訊息給車輛駕駛，將有助於提升駕駛安全與減少交通壅塞。此外，對車輛駕駛若輔以高效能與即時影像廣播之視訊功能，也將大大增加駕駛安全與行車樂趣。然而，因為車輛行經高速公路時常因相對位置快速變化而形成具高移動性之車輛通訊網路環境，因此必須考量諸多相關問題，包含無法形成較長時間之固定網路拓墣及進行多重跳接傳送時多源封包之傳送時程安排等問題。 要解決上述車輛移動性與多重跳接傳送之問題，我們設計了一種傳送多源交通訊息的重疊式網路架構方案。該方案係由一個適應移動之訊息減量方案(IR)及一個適合車輛進行叢集對叢集之多重跳接傳送方法(VAC)所共同組成。所有車輛執行IR方案後將各自有歸屬之叢集，而叢集則作為其所在地交通訊息的傳送代表單位。主要設計目的係為簡化個別車輛的高速移動問題及減少大量的訊息廣播。之後，VAC方法從已形成之叢集頭端與尾端來選擇下一最佳化之中繼節點，以增加多重跳接之傳送效益。在模擬實驗方面，我們定義三種以駕駛人感知程度的客觀量測值並以不同的交通情境對所提方案及其他兩種通信協定進行網路傳送效能的模擬與結果分析。同時，我們更進一步探討所提方案的協定負載狀況、廣播減量比例以及在施行技術上可能產生的誤差值，用以驗證所提方案對交通訊息傳送的的好處與效用。最後，經由模擬結果證實我們所提方案確實對於高速公路上交通安全訊息的傳送提供了一個有效之多源與多重跳接的訊息傳送平台。在適當連接的車輛通訊網路環境中，我們所提方案可有效傳送高度正確之交通安全訊息。 其次，我們針對MPEG-4此種流行的影像串流及車間通訊，發展出一套儘可能瞬間傳送大量封包方式的影像廣播方法，稱之為BEB方法。BEB方法適用於高速公路情境並可克服車輛間高移動性的問題而執行有效的影像多重跳接廣播。BEB方法具備有即時性與分散式的特性且毋須額外通信協定負載。該項方法係由佇列程序與排程方法所構成。佇列程序的功能是將所收到之MPEG-4影像依其訊框相依特性進行整流工作並依傳輸順序將封包排列送至傳送佇列中。而基於佇列程序執行結果，所設計之排程方法則用於計算並安排影像傳送佇列的廣播時間。BEB方法使用的是巨觀的廣播概念，而此概念特別適用於MPEG-4影像串流的傳送，一方面可增加廣播效能及影像收看品質，另一方面則可減少不必要的重覆廣播。在模擬過程中，我們將BEB方法與另一通信協定一起評估比較。模擬時，以不同之廣播情境並採用實際的MPEG-4影像串流來量測訊雜比值(PSNR)及影像訊框掉包率。最後之分析結果，證明我們的BEB方法確實適用於 MPEG-4影像串流的多重跳接廣播並可有效提升高速公路上MPEG-4影像傳送的品質。 上述有關在高速公路環境中的交通安全訊息傳送及MPEG-4影像廣播之解決方案，依據模擬結果顯示，兩者皆可有效地解決高移動性所衍生的問題並且對交通安全與娛樂等與行車相關之應用程式提供有效且快速的多源與多重跳接傳送服務。未來若能將上述提案實際應用於高速公路環境中，將有助提升行車安全與駕駛樂趣。
並列摘要
For inter-vehicle communication (IVC), efficiently propagating adequate and effective traffic information to drivers helps increase driving safety and reduces traffic jams on highways. In addition, by high performance and real-time video broadcasting, the enhanced vision assistance further increases the driving safety and traveling fun for drivers. However, it is hard to structure vehicles into permanent network topologies and schedules to propagate multi-source traffic information and broadcast video streaming real-time in IVC in a high-mobility vehicular environment. To achieve this, firstly we have designed an overlay traffic information solution which considers the challenges of propagating multi-source information caused by vehicle mobility and multi-hop forwarding. The overlay solution is composed of a mobility-adaptive information reduction scheme (IR scheme) and a vehicle-adaptive cluster-to-cluster multi-hop forwarding method (VAC method). The IR scheme creates a mobility-adaptive cluster to represent local traffic information. The purpose of the scheme is to simplify individual high-speed movements and reduce large amounts of information broadcasts. Based on the results of the IR scheme, the VAC method selects the optimal relay node of the inter-cluster forwarding pair to increase the efficiency of multi-hop propagation. In simulation, we compared network performance with two other protocols by defining three objective metrics of driving-perceived quality under different traffic scenarios, and analyzed the results. Furthermore, we explored the protocol overhead, the broadcasting reduction ratio, and technological deviations to verify the advantages and efficiencies of our solution. The simulation proves that our solution is an efficient multi-source and multi-hop forwarding framework that allows well-connected vehicular networks to disseminate a higher degree of correct traffic information, especial for highway safety-related information. Secondly, we have developed a burst effort broadcast (BEB) approach, which considers the features of MPEG-4 video streams to adapt to highway scenarios and overcome the challenges of high mobility and multi-hop broadcast. The BEB approach is distributed real-time without protocol overheads, and comprises a queuing procedure and scheduling scheme. The queuing procedure is of the pre-process of video transmission including the video shaping of groups of pictures (GOPs) and sequentially re-ordering video frames. Based on the queuing procedure, a mobility-adaptive scheduler is applied to process the broadcast and re-broadcast of the video stream. The concept of macroscopic broadcast is for MPEG-4 specific and utilized to increase the broadcast performance and video perceived quality of service (PQoS) as well as to reduce the number of unnecessary redundant broadcasts. As an evaluation, the real MPEG-4 video was conducted in simulation and the broadcast performance was compared with another protocol by the metrics of peak signal to noise ratio (PSNR) and loss of video frames in different broadcasting scenarios, and the results were analyzed. The simulation proved that this approach is an efficient multi-hop broadcast solution that does indeed provide a realistic solution to promote a higher degree of MPEG-4 video PQoS on highways. Both the proposed solutions are highly adaptive to high mobility and capable of effective and efficient multi-hop transmission on traffic information and video streams on highways for the safety-related and infotainment IVC applications, and therefore, the practice of the proposed solutions will be beneficial for increasing the driving safety and comfort in the future.