適用於IEEE 802.11無線區域網路電話系統中之省電傳送機制

Abstract

無線區域網路電話(Voice over IP over WLAN, VoWLAN)為公眾與私人無線區域網路系統中一項重要的應用服務。然而，這樣的服務面臨了手持裝置耗電與系統能支援的最大使用者數目(VoWLAN Capacity)有限等技術挑戰，因此使得大規模的商業化佈建緩慢。在本研究中，我們針對IEEE 802.11無線區域網路電話系統提出了一個跨層的省電傳送機制，此機制考量語音封包可以忍受某種程度封包遺失(packet loss)的特性，並且根據目前語音封包遺失率，動態的停用媒體存取控制層(MAC)對於語音封包的回應封包(Acknowledgement)。在此機制下，可以縮短手持裝置傳送與接收封包所需的時間與對應消耗的能量。模擬結果說明瞭本機制可以在通話品質被保證的情況下，大幅的改善無線區域網路手持裝置的耗電情形，以及無線區域網路電話系統所能支援的最大使用者數目。

Voice over IP (VoIP) over WLAN (VoWLAN) is an important application for public and private WLANs. However, VoWLAN systems suffer from various technical challenges such as power consumption of WLAN stations (STAs) and VoWLAN capacity issues, making the commercial deployment of large-scale VoWLAN services problematic. This study presents a cross-layer and energy-efficient mechanism for transmitting VoIP packets over IEEE 802.11 WLANs. The proposed mechanism considers the characteristics of VoIP that can tolerate some packet loss, and dynamically disables the medium access control (MAC) layer acknowledgement for voice packets according to the packet loss rate. In doing so, the time and energy consumed to transmit and receive voice packets for a VoWLAN STA can be reduced. Simulation results demonstrate that the mechanism significantly improves the energy efficiency of a VoWLAN STA and WLAN utilization while the voice quality can be also guaranteed.