IEEE 802.11e無線區域網路下針對VoIP話務之高能源效率媒體存取控制協定

Abstract

在無線網路環境下對於VoIP攜帶式裝置，如何節省能源是一個重要的問題。在本論文中，我們提出了一個與IEEE 802.11e相容的高能源效率媒體存取控制協定(PEP)去改進原有的ODP機制。在ODP機制裡，當基地台收到連續兩個QoS Null訊框，就會將其對應的語音用戶站從輪詢表中移除。PEP機制結合HCF中輪詢機制(HCCA)和競爭機制(EDCA)。基地台動態地維持輪詢表。我們假設在輪詢表中的所有語音用戶站皆是處於主動模式。當語音用戶站傳送Null訊框裡的貯列大小值為零，並且仍有剩下的TXOP時，其語音用戶站會被視為進入寂靜模式，此語音用戶站將會自輪詢表中被移除。此語音用戶站可在EDCA競爭週期裡尋求再加入到輪詢表中。為了增加預測語音用戶站進入寂靜模式的準確性，在PEP機制裡加入了一個評估TXOP利用率的啟發式方法。模擬結果顯示關於能源消耗方面，在沒有犧牲網路產量的情況下，PEP機制比RRP和ODP機制分別節省了24.5%到37.1%和12.9%到15.1%的能源。

Power saving is a critical issue for VoIP over WLANs, especially when using handheld devices. In this thesis, we present an IEEE 802.11e compatible power-efficient MAC protocol to improve the on-demand polling (ODP) scheme. In the ODP scheme, if two consecutive QoS Null frames are received by a QoS AP (QAP), the corresponding QoS station (QSTA) will be removed from the polling list. The proposed Power-Efficient Polling (PEP) scheme uses both the polling-based (HCCA) and contention-based (EDCA) channel access over the hybrid coordination function (HCF) mechanism. A QAP maintains a polling list dynamically. All QSTAs in the polling list are assured active. When a QSTA sends a NULL frame with a queue size of zero and the allocated transmission opportunity (TXOP) is not used up, the QSTA will be regarded as entering the silence period. The QSTA will be removed from the polling list. The QSTA can join the polling list again during the contention-based period of EDCA. In order to increase the prediction accuracy of a QSTA entering the silence period, a heuristic method to evaluate the utilization of allocated TXOP is added to the PEP scheme. Simulation results show that the PEP scheme in terms of normalized power consumption outperforms the RR and ODP schemes from 24.5% to 37.1% and 12.9% to 15.1%, without sacrificing the throughput.