IEEE 802.11e 無線區域網路下針對VoIP話務之省電式媒體存取控制機制

Abstract

在近年來的網際網路應用中，網路電話因為具有許多優於傳統電話的特性：低通信成本、高頻寬以及易於創造新的服務，使得它已成為最吸引人的應用之ㄧ。然而，當網路電話被應用在無線區域網路的環境時，語音用戶的能源消耗成為了一個關鍵的議題。在本論文中，我們提出了一個在IEEE 802.11e無線區域網路下針對VoIP話務之省電式媒體存取控制機制 (PSM-V)。PSM-V的基本概念是在EDCA機制中加入一段免競爭的期間給語音用戶使用。我們利用信標訊框去定期地發佈一個TDMA的存取排程表，使語音用戶能夠遵循。這個存取排程表可以讓語音用戶去避免封包的碰撞和減少語音用戶的閒置時間。模擬結果顯示，我們提出的PSM-V相較於U-APSD方法(包含在IEEE 802.11e標準內)[1]與U-APSD-M方法[2]，在以語音用戶的平均責任週期來評估其能源效率上，分別改善了51%與17%。模擬結果也顯示，PSM-V相較於U-APSD與U-APSD-M，平均增加了63%與8%的總產量以及減少了34%與20%的平均封包延遲時間。總結來說，PSM-V在其系統容量內，能夠有效改善語音用戶的能源效率，並且能確保話務的產量與延遲效能不會被降低。

Among recent internet applications, Voice-over-IP (VoIP) is one of the appealing ones due to its advantages over traditional telephony, such as low communication cost, high bandwidth and easy creation of new services. However, when it is applied to wireless local area networks (WLANs), power consumption becomes a critical issue for voice stations (handsets) in the network. In this thesis, we propose a power saving MAC mechanism for VoIP applications (PSM-V) based on the IEEE 802.11e EDCA. The basic idea of PSM-V is adding a contention-free period for voice traffic in the EDCA mechanism. We utilize a beacon frame to periodically announce a TDMA access schedule for voice stations to follow. The access schedule can allow voice stations to avoid voice packet collisions and to reduce station idle time. Simulation results show that the proposed PSM-V improves the energy efficiency of voice stations over the U-APSD approach, which has been included in the IEEE 802.11e standard [1], and the U-APSD-M approach [2] by 51% and 17% in terms of average duty cycle, respectively. The simulation results also show that PSM-V improves the aggregate throughput of voice traffic over U-APSD and U-APSD-M on average by 63% and 8%, and it reduces the average delay of voice traffic over U-APSD and U-APSD-M on average by 34% and 20%. In summary, PSM-V can guarantee that while improving the energy efficiency of voice stations, the throughput and packet delay performance of the voice traffic will not be degraded under the system capacity.