在無線隨意網上提供語音/數據服務之高節能效率媒體存取層協定

Abstract

為了延長使用電池供電無線網路設備之運轉時間，IEEE 802.11訂定了標準的同步式電源管理機制。由於工作站間彼此的時間必需同步化，因此在IEEE 802.11標準中有針對IBSS(Independent Basic Service Set)規定一套分散式同步電源管理機制TSF(Time Synchronous Function)，以達到不需外加同步設備即可達到同步的目的。 在IEEE 802.11電源管理機制中，時間是被切割成一段段的Beacon Interval，在每個Beacon Interval的起始段，每個工作站都必須醒來一段固定時間稱為ATIM Window，在這段時間裡如果工作站沒有資料要傳送或接收，將會在Data transmission Window時進入睡眠狀態，從許多研究顯示ATIM Window大小對MAC層省電效率及整體網路的效率有相當大的影響。 本論文設計一可以提供語音/數據之高節能效率媒體存取協定並提供服務品質保證。我們將使用頻寬保留機制在語音傳送上，一但工作站在ATIM Window中成功完成ATIM 訊息交握，工作站將不必要在ATIM Window中競爭發送ATIM 訊息，即可在Data transmission Window中傳送語音封包。本論文也提出可隨負載流量動態調整ATIM Window 大小的方法，並且改善頻道使用率。本論文也同時讓工作站僅需要在Data transmission Window中傳送資料時醒來，以減少工作站醒來時間及切換次數。

To prolong the network operating time of battery-powered wireless LAN devices, this work proposes a synchronized power management scheme specified in IEEE 802.11 standard. The proposed synchronous protocol requires precise time synchronization among all participating nodes within the Independent Basic Service Set (IBSS). Therefore, Time Synchronization Function (TSF) is defined to enable the protocol to operate without external timing sources. In the proposed 802.11 power management scheme, time is divided into so-called beacon intervals. At the start of each beacon interval, each node must stay awake for a fixed time-period called an ATIM window (Ad-Hoc Traffic Indication Map window). Nodes that have no data to send or receive during the ATIM window enter the doze state in the data transmission window. Many studies indicate that ATIM window size significantly affects power saving and throughput achieved by the nodes. This thesis introduces an energy-efficient MAC protocol to support CBR Voice and Data. Overall Quality of service (QOS) is guaranteed. A bandwidth reservation scheme can be used for CBR Voice transmission. Once stations finish the ATIM message exchange in ATIM window, stations transmit CBR Voice packets in the Data transmission window without further ATIM contention. The proposed protocol improves bandwidth utilization to dynamically adjust ATIM window length to the traffic load. Stations are also allowed to stay awake for only a fraction of the Data window which reduces switch-over time in the Data transmission window.