https://scholars.lib.ntu.edu.tw/handle/123456789/150269
標題: | 在802.11之存取層下以群為基之可擴充高效能分散協同函數(DCF)與低電耗DCF之設計與分析 Design and analysis of a scalable, high-performance grouping-based DCF and a low power DCF in the MAC layer of 802.11 |
作者: | 丁國章 Ting, Kuo-Chang |
關鍵字: | 802.11;802.11n,;MAC capacity;DCF;DIFS;idle listening;802.11n | 公開日期: | 2009 | 摘要: | 無線網路802.11已經凌駕其他技術,已經成為受歡迎之存取網際網路之協定。但此技術並不具擴充性,因為當active stations 數目增加時,由於必須付出高昂的碰撞代價,存取層之效率(Capacity)會大幅降低。本論文將提出一個以群為基,高效能之分散式協同函數(HG-DCF)[29, 30]。也就是引進分時存取(TDMA)之概念,把所有active stations 分成數群,以避免所有stations同時傳送訊框,並據以降低傳統802.11之DCF之大且固定之傳送負擔如ACK,並增加存取層之效率。HG-DCF 之概念源於,DIFS, SIFS,與ACK 加到群循環中,也就是所有的group slots,而非每一個資料訊框皆須此固定且大之負擔。而AP可以依據此群循環來作此集體回應(Block-ACK)。我們的研究分析指出,HG-DCF 在傳統較低速之802.11下,其capacity 可以達93.8,此效率甚至比802.11之DCF之理論極限值91.4%還大到2.4%。此種改善程度,會隨未來之無線網路標準之實體層速度之增加,而增加。最新之802.11n之實體層速率可達600Mbps,研究與分析顯示HG-DCF之存取層之效率可以達22.9%,然而DCF之理論極限值只有,14.4%,也就是HG-DCF比傳統802.11之DCF 之理論極限值高達60%. 此以群為基之技術可以應用在任何以DCF為基之協定,如EDCA(加強的分散頻道存取),因此可以得到HG-EDCA. 模擬結果顯示HG-EDCA可以解決一般DCF之語音傳送跳動問題,在本論文中一種新的分群技術[45]被提出,並予以分析與模擬此技術之分群整齊性,並避免空的群時區發生,也就是沒有一個active station屬於此群,並提高分群之整齊性與公平性,面對在未來極高速之802.11n無線網路,此技術還可以增加存取層之效率(capacity)。802.11之能源效率方面,由於也因為有很多固定之負擔在於傾聽DIFS 與Back-off 期間時之閒置頻道,而傾聽閒置頻道時,必須把收發器打開,所以其所消耗之能源與接收所需能源所差無幾,故能源效率很差,尤其以未來之802.11n為甚。在本論文中針對802.11n之DCF 提出一個聰明的傾聽機制用於減低傾聽所需之能源。研究之分析與模擬顯示,此方法可以延長電池的壽命達3倍。此論文中也將提起一個精確的,基於存取層上的能源分析模式,而此分析模式除了[46],並未出現在之前之所有研究中。 Today’s 802.11 Wireless Local Area Network (WLAN) technology has prevailed over other technologies and has become a popular protocol for Internet access. However, this technology is not scalable at all because its capacity will deteriorate with an increase in the number of active stations, due to the huge collision costs involved. In this thesis, we propose a high performance Grouping Distributed Coordination Function (HG-DCF) based on [29, 30] which introduces the TDMA concept to partition all active stations into several groups to prevent all stations from transmitting frames simultaneously and to reduce the heavy overhead of legacy DCF and to increase the MAC layer efficiency of the 802.11 protocol. The key idea behind HG-DCF is that the Distributed Inter-Frame Space time (DIFS), Short Inter Frame Space time (SIFS), and Acknowledge (ACK) frames are added to the grouping cycle, which consists of the transmissions of all groups’ slots instead of a single frame. Block-ACK performed by the AP is based on this grouping cycle. Our analysis shows that the capacity of our HG-DCF could reach 93.8%, which is 2.4% larger than the theoretical capacity limit of 802.11 WLAN of 91.4%, even if the distribution of active stations among all groups is not completely uniform. This improvement will increase as the data rate increases or the frame size decreases due to the shorter data time and this capacity can be independent of the number of active stations and the contention window maximum (CWMax). Our research shows that If the data rate is up to 600 Mbps, the capacity of HG-DCF can be up to 27.17% if the new partition scheme shown in this thesis is applied. On the contrary, the capacity limit of DCF with the same scenario is only 14.4%, and thus this improvement can be up to (22.9-14.4)/14.4%?60%. This grouping technique can also be applied to any DCF-based protocol such as EDCA (Enhanced Distributed Coordination Access) to get the high performance grouping EDCA, denoted as HG-EDCA. Simulations show that HG-EDCA solves the delay jittering problem. A new group partition technique is also proposed, analyzed and simulated in this article to avoid the scenarios with empty group slots and to keep the distribution of the group sizes of HG-DCF more uniform. n the other hand, the energy efficiency of 802.11 is very poor is also due to these heavy overheads in idle listening to the idle channel during the DIFS and back-off and the energy consumed for idle listening is similar to the energy consumed while receiving data [41]. In this thesis, an intelligent scheme for reducing the energy consumed in idle listening is proposed. Our analysis and simulation programs show that our scheme can lengthen the battery endurance up to 3 times due to the shortening in idle-listening time effectively especially when the number of active stations is large. An important characteristic of our scheme is that it is fully compatible with legacy Distributed Coordinated Function (DCF), and there will be no throughput reduction if this power saving scheme is applied to the DCF of 802.11. We also propose an accurate power consumption model in the MAC layer which to the best of our knowledge has not been presented in any earlier research except [46]. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/188007 |
顯示於: | 電機工程學系 |
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ntu-98-D92921019-1.pdf | 23.32 kB | Adobe PDF | 檢視/開啟 |
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