IEEE 802.16e/m 網路中VoIP有靜默壓縮之排程增強

Abstract

在語音通訊中會有靜默聆聽對方講話的時候，此時利用網路電話有靜默壓縮(VoIP with silence suppression)的技術可以節省靜默時的傳輸頻寬。當使用者從靜默回復成講話狀態，使用者應該立即獲得頻寬分配，才能重新傳輸語音封包。在全球互通微波存取無線網路 (Worldwide Interoperability for Microwave Access, WiMAX) 中用戶端(Subscriber Station, SS) 改變VoIP頻寬需要對基地台(Base Station, BS)送出頻寬要求(Bandwidth Request)，在WiMAX中常用的頻寬要求方法有分單獨輪詢(Unicast polling)及群播輪詢(Multicast polling)。單獨輪詢的傳輸延遲是有保證的，但是用在詢問的負擔較大，而群播輪詢的負擔較小但是可能發生碰撞造成延遲沒有保證。一個重要的問題是如何在延遲及詢問負擔中做取捨以達成系統較好效能。 在我們的研究中提出了混合型頻寬要求的方法給VoIP有靜默壓縮，結合了單獨輪詢及群播輪詢，提供了延遲保證及較小的輪詢負擔。我們可以透過設計單獨輪詢及群播輪詢的週期及群播輪詢所用的競爭資源大小，達成較小的輪詢負擔及較佳的傳輸延遲，進而增加語音通信的使用人數的容量。 這篇論文研究的主要貢獻是使用較低的輪詢負擔在確保延遲下，增進VoIP的使用人數。

When people make voice communications, one person listens while the other speaks. At the listening time the bandwidth can be saved by using silence suppression technique in the VoIP. In VoIP with silence suppression service, when the user transits from silence state to talk-spurt state, the user should obtain bandwidth allocation as soon as possible. In IEEE 802.16 WiMAX, the general methods of bandwidth request (BR) are unicast polling and multicast polling. The unicast polling can guarantee delay performance but has high overhead for polling. Differently the multicast polling has low overhead, but the access delay cannot be guaranteed. An essential issue is to improve the tradeoff between the access delay and the polling overhead. In this thesis, we propose a hybrid bandwidth request (combining unicast and multicast polling BR) method for providing VoIP services with silence suppression to subject to the delay constraint from silence to talk, while reducing the overhead for polling. We design the intervals of the unicast and multicast polling and the contention resource of multicast polling to improve the tradeoff between improving delay performance and reducing overhead. In summary, the main contribution of this thesis is to improve the capacity of VoIP users by lower polling overhead, while ensuring delay performance.