無線寬頻接取組播廣播服務區域□的可靠同步方法 – 用WiMAX 為例子

Abstract

WiMAX是希望提供給大範圍內大量行動用戶高速傳輸速率的無線寬頻網路協定。在WiMAX裡，MBS-Zone是由一群同步的基地台所組成，被採用來提供給用戶組播廣播服務。在同一個MBS-Zone底下，使用者可以隨意的移動而不需要進行換手的機制並且可以從多個基地台同時接收MBS資料，提供了巨多分集(Macro Diversity)的效應。巨多分集效應可以抵抗干擾近而增加MBS-Zone的吞吐率。在最新的WiMAX標準裡已經定義了基地台同步的架構。在同步的處理過程中使用了名為同步規則(Sync Rule)的控制訊號。同步規則包含了一些進行同步化時會用的參數，由同步控制中心(Sync Controller)送給所有的同步執行者(Sync Executer)。在傳輸同步規則時可以使用單點傳播或是組播的方式傳送。單點傳播的方式雖然可以保證可靠性但是傳輸的效率卻不好，相反的組播有較好的傳輸效率但是卻不保證可靠性。因此我們提出了一個新的可靠組播方式來傳送同步規則。在同一個MBS-Zone底下我們把所有的SE分割成好幾個”傳送區域”群組，每個群組有一個唯一的領導者。透過領導者來幫忙重送同步規則可以使的傳送區域的群組得到local recovery的效果進而有效地減少同步規則的重送延遲。模擬跟分析的結果顯示我們的方法比目前WiMAX標準裡所提到傳輸方法有更好的效率。不只提供了傳輸的可靠並且減少了重傳的延遲。

WiMAX is a broadband wireless network protocol that promises to transmit high data rate over large areas to a large number of mobility users. In WiMAX, MBS-Zone is introduced for providing Multicast Broadcast Service (MBS) to the group of receivers among multiple synchronized BSs. In an MBS-Zone, MSs can benefit from the handover-free and the macro-diversity gain by receiving multiple signal paths from more than one BS. Macro-diversity gains the robustness of anti-interference which can improve the throughput of MBS-Zone. In the latest WiMAX specification, MBS-Zone synchronization architecture is already defined. In the process of synchronization, a control signal ''Sync Rule'' that includes synchronization parameters needs to be transmitted from Sync Controller (SC) to all Sync Executers (SEs). Unicast or multicast can be adopted for transmitting Sync Rules; however, unicast is reliable but inefficient, whereas multicast is efficient but unreliable. Therefore, we propose a novel reliable multicast scheme to transmit Sync Rules. For SEs located within the same MBS Zone, this scheme requests to divide them into many groups, named “retransmission zones”, and every group has a unique leader. The leader of each retransmission zone benefits the ability of local recovery which can reduce the Sync Rule retransmission delay efficiently. Simulation and analysis results demonstrate that our work outperforms other approaches proposed in WiMAX MBS specification. The advantages do not only guarantee the transmission reliable, but also improve the latency of retransmitting Sync Rule.