在IEEE 802.16e下一個節省能源的增進型睡眠模式運作方式

Abstract

近年來，無線寬頻網路(如IEEE 802.16e)已經有愈來愈受歡迎的趨勢。對於在無線寬頻網路的的行動用戶來說，所有的運作都依賴著有限的電池能源，該如何節省能源是一個重要的問題。行動用戶被允許可以進入睡眠模式，以達到節省電源消耗的目的。在IEEE 802.16e中，它將所有的連線服務依照省電的運作方式，分成三種不同的省電類型(I, II 及 III)。一般而言，在基地台和行動用戶之間，可能存在著一條以上的連線服務。為了更有效率的省電，我們必須同時考慮所有的連線服務。在本論文中，我們只考慮單一播送的連線服務。我們去除了在省電類型I中的聆聽視窗，同時考慮在延遲限制下，聚集數個省電類型II的封包並延遲在同一個訊框中傳送，這樣可以減少類型II的聆聽視窗個數。而在類型II的聆聽視窗中，行動用戶可以收到所有連線服務的MOB_TRF-IND訊息。藉由減少聆聽視窗的個數，行動用戶可以在所有的連線服務中，得到更多的共同空閒時間，因此可以停留在睡眠模式下更久。如果有愈長的睡眠時間，則行動用戶就可以達到更好的省電效果。模擬結果顯示，關於能源消耗方面，我們提出的方法(E-LCFT)比IEEE 802.16e的方法，可以提高33%到68%的省電效果，但是相對地有比較長的封包延遲時間。即使如此，我們的方法依然滿足了類型II的QoS(延遲)需求。我們所提出的方法和原有的IEEE 802.16e標準依然相容，因為我們的方法只需要調整基地台的類型I 和類型II之睡眠視窗參數，並沒有更改到其它的協定。

The broadband wireless access (BWA) network, such as IEEE 802.16e, becomes more and more popular in recent years. The power saving for mobile subscriber stations (MSSs) in this network is a very important issue, because all MSSs operate on the limited battery power. The MSSs are allowed to switch to the sleep mode to reduce their power consumption. In the IEEE 802.16e, it classifies service connections into different types of power saving classes, types I, II and III, for power saving operation. In general, there may be more than one service connection between a base station (BS) and an MSS. For efficient power saving, we have to consider all service connections as a whole. In this thesis, we focus on unicast service connections only (types I and II). We eliminate the listening windows of the power saving classes of type I. We also group several type II packets into a single frame for transmitting later while meeting its delay constraint. This is to reduce the number of listening windows of the power saving classes of type II. During the listening windows of type II, the MSS will receive the traffic indication (MOB_TRF-IND) message of all types. In this way, the MSS can have more common free time among service connections in order to stay in sleep mode longer. The longer the sleep periods is the more power saving the MSS can achieve. Simulation results have shown that our proposed E-LCFT (enhanced longer common free time) performs 33% to 68% better than the IEEE 802.16e Standard in terms of percentage of sleep periods, which reflects power consumption. The overhead of the proposed E-LCFT is that it has longer average packet delay than the IEEE 802.16e Standard. However, the QoS requirements of type II connections are still guaranteed. The proposed E-LCFT scheme is still compatible to the IEEE 802.16e Standard, because our schemes only need to adjust the sleep windows of types I and II.