- 學位論文
無縫交遞之數位影像多點傳送系統
Digital Video Multi-casting System with Seamless Handover Mechanism
摘要
自歐洲電信標準組織（ETSI）制定DVB-H規範後，數位電視即邁入手持式應用的領域。唯現行之手持式裝置，如個人數位助理（PDA）或智慧型手機（smart phone）需額外設備才能使用，相對而言，大多數的PDA都有內建WLAN （IEEE 802.11b），如果能將DVB-H服務接收轉換，播放在WLAN環境，即可在捷運或大樓等室內提供數位電視服務。當手持式裝置在室內環境移動時，可能會需要進行交遞（handover）動作，交遞會使正在傳送的資料遺失，進而影響到所提供的多媒體服務品質，因此為了維持良好的服務品質，本文提出一種用於數位影像播放的無縫交遞（seamless handover）方式，用以解決此問題。 本文主旨為設計以WLAN為傳遞媒介，採用多點傳送（Multicast）傳送方式，利用Multicast傳送資料只需傳送一次即可讓複數手持式裝置接收的特點，配合時間切片機制，將傳送資料後的關閉時間（Off-time）用來偵測網路環境，達到軟式交遞（soft handover）的目的，交遞期間不會造成遺失資料，可達到無縫交遞。 為了進一步證明本文所提出知無縫交遞機制的可行性，故在微軟公司的 .NET framework 2環境並採用Visual C# 作為開發語言，實做具時間切片功能的串流主機及軟式交遞機制的串流接收器，採用PDA為手持式裝置，作為測試環境來實現數位影像多點傳送之無縫交遞。 經由實驗結果得知，於播放有交遞的過程之封包遺失率為0.589%，相較於PDA固定在RSSI –40 dB環境的封包遺失率0.436%，沒有明顯的增加，可證明採用此方法達到無縫交遞的可行性。
並列摘要
Since the European Telecommunications Standards Institute (ETSI) developed the DVB-H standard, digital TV is entering the field of handheld applications. But the existing handheld devices, such as personal digital assistants (PDA) or smart phones require additional equipment to use. Relatively speaking, most PDAs have built-in WLAN (IEEE 802.11b). If we can convert DVB-H services after receiving, then broadcasting over the WLAN environment. We can provide digital TV services in building such as the museum or indoor. When the handheld device moving in the indoor environment, we may need to handover which cause transmitted data loss. Thereby affecting the quality of multimedia services, in order to maintain good service quality. This thesis presents a digital video multi-casting system with seamless handover mechanism to solving this problem. The purpose of this thesis is to design for WLAN enviroment with multicast transmission. Use the characteristics of multicast, need only send one can let a few handheld devices receive. With timeslicing mechanisms, use the Off-time to detect network environment to perform soft handover. The handover period will not cause loss of information for seamless handover. To further prove the seamless handover mechanism feasibility. We use Microsoft .NET framework 2 environment with Visual C # development language. We have done a timeslicing streaming server and soft handover streaming receiver. Using PDA for handheld devices, as a test environment to achieve digital video multicast system with seamless handover mechanism. By the experimental results, the packet loss rate is 0.589% when handover during playing. In contrast to the packet loss rate of 0.436% when fixed PDA in RSSI -40 dB environment. There was no obvious increase so can prove that use of this method to achieve seamless handover feasibility.