IEEE 802.11e HCCA 中改善傳輸效能之動態排程演算法
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2008
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Abstract
在IEEE802.11e的修正草案中，提出了根據平均的封包大小和資料產生率來計算TD (TXOP Duration)及SI (Service Interval)的演算法，但卻無法適用於VBR (variable bit rate)資料流。因此，在相關研究裡提出一個TXOP timer的機制，利用可變的輪詢週期以及可變的TD來適應VBR的資料型態。此外在TXOP timer 的基礎上，更有研究提出了利用佇列的資料量資訊QS (Queue Size)來分配準確的TXOP。雖然在TXOP配置方面可因此接近於完美，但在資料流量控管方面仍然有很大的改善空間。這是因為TXOP timer的增長速率為一平均值，因此在服務VBR封包時會導致若干封包無法在延遲範圍內接受服務。本論文將提出一個有效的排程演算法來改善TXOP timer機制，而作法主要是將QSTA (QoS Station)的服務分成輪詢及傳送兩部分。在輪詢部分將使用VBR最短的服務區間以準確的掌握VBR的封包產生時間；在傳送部分針對TXOP timer的傳輸限制提出無timer傳輸條件以及根據QS調整之變動timer傳輸條件來改善傳輸效能。經由模擬發現本論文作法可以有效的改善封包的延遲及遺失，並且能達到較高的吞吐量。
In IEEE 802.11e, the provision of parameterized quality of service (QoS) is enabled by a polling-based scheduling. The scheduling deals with assignments of transmission opportunities (TXOPs) to QoS stations (QSTAs) at proper polling time instants, and it is inefficient for variable bit rate (VBR) traffic streams if both of the TXOP durations and the polling instants are estimated based on mean values declared in the respective traffic specifications (TSPECs). Although the efficiency can be improved by adapting TXOP durations according to the backlogged traffic reports issued by QSTAs, a problem still remains if polling instants are determined by mean-value timers. In this paper, we first point out the performance impairment that may be caused by mean-value timers, then a traffic scheduling algorithm using an adaptive timer is proposed to remedy this problem.
In IEEE 802.11e, the provision of parameterized quality of service (QoS) is enabled by a polling-based scheduling. The scheduling deals with assignments of transmission opportunities (TXOPs) to QoS stations (QSTAs) at proper polling time instants, and it is inefficient for variable bit rate (VBR) traffic streams if both of the TXOP durations and the polling instants are estimated based on mean values declared in the respective traffic specifications (TSPECs). Although the efficiency can be improved by adapting TXOP durations according to the backlogged traffic reports issued by QSTAs, a problem still remains if polling instants are determined by mean-value timers. In this paper, we first point out the performance impairment that may be caused by mean-value timers, then a traffic scheduling algorithm using an adaptive timer is proposed to remedy this problem.
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排程, 無線網路, IEEE 802.11e, scheduling, WLAN, IEEE 802.11e