本論文針對在同一時間、同一地點觀看同一串流影片的一組用戶，例如家庭或幾個朋友在公車上或火車上旅行，提出了基於多接取邊緣計算(MEC)架構的品質自適機制之1-to-k協同SVC串流方法。在所提出的方法中，選擇組成員中的一手持裝置作為組頭之手持裝置（H-HD），它負責（i）使用 4G/5G 行動網絡從 MEC 服務器下載影片內容 x，然後（ii) 使用D2D通信方式將下載的影片x內容多播到其他組員的接收之手持裝置（R-HD），其中H-HD 和 R-HDs之間透過Wi-Fi網絡傳輸影片內容和訊息。在所提出的方法中，估計頻寬是根據所有 R-HD 的接收資料傳輸速率及過往的估計頻寬並透過指數加權移動平均 (EWMA) 方式計算。再者，針對具有估計頻寬的多播環境並結合所提出的自適應前向錯誤更正 (FEC) 方案，可以計算出符合下一個傳輸週期中適應的影片資料傳輸率，該方案可以解決數據包傳輸錯誤問題。為了實現流暢的影片串流播放，提出的當前下載區段(CDSS)機制能根據網絡情況、影片播放情況和緩衝情況動態調整其區段大小，使得在一個CDSS下載週期內的所有影片片段可以同時被考慮下載。另外，根據網絡情況、影片播放情況和緩衝情況定義了兩個動態調整的閾值來決定接下來將下載CDSS中的哪個影片片段的對應影片質量，這兩個閾值分別用於限制（i）當前正在下載的影片片段及其前一個影片片段之間的質量差異以及 (ii) 當前正在下載的影片片段及其下一個影片片段。為了最大化多播群組的整體服務時長，並解決貢獻平衡問題，每個成員的手持裝置須輪番擔任H-HD。本論文提出了一種信用方案，根據當前H-HD在一輪下載中消耗的電池電量、下載的數據量和其剩餘電池電量，計算每個R-HD需要向H-HD支付多少信用值；另外，當前信用值最低的成員將擔任下一輪的H-HD。性能評估結果表明（i）所提出的品質自適機制SVC串流方法可以減少影片質量切換的頻率，更有效地利用網絡頻寬來提高多播環境下的播放質量； (ii) 基於信用導向的 H-HD 切換機制可以在所有群組成員的手持裝置中實現更均勻的資源消耗，從而延長該多播群組的協同下載時長。

This thesis proposed the 1-to-k cooperative SVC adaptive streaming method for a group of users, who are watching the same video at the same time and in the same place, e.g., several friends who are having a journey in the bus or train, based on the Multi-access Edge Computing (MEC) architecture. In the proposed method, a group member’s handheld device is selected as the Header Handheld Device (H-HD), which is in charge of (i) downloading the video content x from the MEC Server using the 4G/5G cellular networks and then (ii) multicasting the downloaded video content of x to the other group members’ Receiver Handheld Devices (R-HDs) using the Device-to-Device (D2D) communication way, for which the Wi-Fi network is adopted for the communication among H-HD and R-HDs. In the proposed method, the estimated bandwidth is calculated based on the received bit rates of all R-HDs and the historical estimated bandwidth using the Exponentially Weighted Moving Average (EWMA) way. Then, the video bit rate that can be adopted in the next transmission cycle is derived by combining the proposed adaptive Forward Error Correction (FEC) scheme, which can tackle the packet error problem, for the multicast environment with the estimated bandwidth. To have the smooth streaming, the Currently Downloading Segment Section (CDSS) mechanism, which can be moved forwardly and whose size can be dynamically adjusted depending on the networking situation, the video playout situation and the buffering situation, was proposed such that the segments inside CDSS can be downloaded at the same time, i.e., in a downloading cycle. Additionally, two dynamically adjusted thresholds depending on the networking situation, the video playout situation and the buffering situation are defined to decide which quality level the currently downloading segment can download, for which the two thresholds are to restrict the quality difference between (i) the currently downloading segment and its previous segment and (ii) the currently downloading segment and its next segment respectively. To maximize the overall service time of the multicast group and resolve the fairness concern, each member’s handheld device can play the H-HD alternatively. A credit scheme was proposed to calculate how much credit each R-HD needs to pay to H-HD based on the consumed battery power, the downloaded data volume and the remaining battery power of the current H-HD in a downloading round; then, the one that has the minimum credit became the H-HD in next round. The performance evaluation results have shown that (i) the proposed streaming method can reduce the frequency of video quality switching and utilizes the network bandwidth more effectively to improve playback quality in the multicast environment; (ii) the credit-based H-HD’s re-selection can have the more even power consumption among all group members’ handheld devices and thus can extend the group’s streaming service time.

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