本文關(guān)鍵詞：基于信道協(xié)同掃描技術(shù)的WiFi網(wǎng)絡(luò)MAC層切換機(jī)制　出處：《長(zhǎng)安大學(xué)》2016年碩士論文　論文類型：學(xué)位論文

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【摘要】：基于IEEE802.11系列標(biāo)準(zhǔn)的無(wú)線wifi技術(shù)已經(jīng)廣泛應(yīng)用于無(wú)線局域網(wǎng)的接入服務(wù),各大運(yùn)營(yíng)商在全國(guó)多個(gè)城市提出開展”無(wú)線城市”計(jì)劃,將無(wú)線局域網(wǎng)與其他移動(dòng)通信網(wǎng)絡(luò)GPRS、3G、LTE等網(wǎng)絡(luò)融合,為整個(gè)城市提供隨時(shí)隨地隨需的無(wú)線網(wǎng)絡(luò)接入服務(wù)。由于無(wú)線訪問(wèn)接入點(diǎn)(Access Point,AP)的信號(hào)發(fā)射功率比較有限,其覆蓋范圍受到限制。移動(dòng)終端(Mobile Terminal,MT)需要在多個(gè)AP之間切換,而切換過(guò)程中所帶來(lái)的較大的切換時(shí)延將顯著地影響諸如VoIP之類的實(shí)時(shí)性服務(wù)的質(zhì)量。本文主要針對(duì)大規(guī)模部署的無(wú)線WiFi網(wǎng)絡(luò)在用戶密集時(shí)MT切換引發(fā)的服務(wù)質(zhì)量下降問(wèn)題開展研究,通過(guò)引入輔助節(jié)點(diǎn)協(xié)同掃描可用信道,降低切換時(shí)延,提高終端在多AP切換環(huán)境下的連接可靠性與實(shí)時(shí)性。本文所作的主要研究工作如下:(1)分析了MT在MAC層的切換過(guò)程及其時(shí)延成因,對(duì)其中最耗時(shí)的探測(cè)掃描階段的時(shí)延產(chǎn)生及改善機(jī)理進(jìn)行了研究,提出了基于信道協(xié)同掃描技術(shù)的WiFi網(wǎng)絡(luò)MAC層切換方法并對(duì)其流程進(jìn)行了描述;(2)在MT啟動(dòng)MAC層切換過(guò)程之前,設(shè)計(jì)了采用接入AP的信號(hào)強(qiáng)度閥值觸發(fā)的預(yù)掃描過(guò)程,針對(duì)實(shí)際場(chǎng)景中可用輔助掃描節(jié)點(diǎn)的不確定性,提出了距離優(yōu)先的輔助節(jié)點(diǎn)選擇算法;(3)同時(shí),對(duì)于掃描過(guò)程中的鄰道干擾問(wèn)題,提出了選擇性并行信道協(xié)同掃描算法,該算法在進(jìn)行分布式探測(cè)的同時(shí),利用MT收集輔助節(jié)點(diǎn)響應(yīng)的AP信息,實(shí)現(xiàn)了切換輔助信息的高效收集;(4)為進(jìn)一步提高M(jìn)T在歷史AP間的切換速度,提出了一種使用最近AP列表高速緩存的方案。該方案能有效避免較短時(shí)間間隔內(nèi)重復(fù)掃描次數(shù),減少掃描時(shí)延。通過(guò)NS-2仿真軟件部署大量的移動(dòng)節(jié)點(diǎn),在引入信道協(xié)同掃描等算法的基礎(chǔ)上對(duì)WiFi網(wǎng)絡(luò)中的切換進(jìn)行了測(cè)試。實(shí)驗(yàn)結(jié)果表明,本文所提切換方案能夠有效減少切換時(shí)延,改善諸如VoIP、視頻流傳輸?shù)葘?shí)時(shí)應(yīng)用的服務(wù)質(zhì)量。
[Abstract]:Wireless wifi technology based on IEEE802.11 series standards has been widely used in wireless local area network access services, the major operators in many cities in the country to carry out the "wireless city" program. The wireless local area network (WLAN) is integrated with other mobile communication networks, such as GPRSU 3G / LTE and so on. The wireless network access service is provided to the whole city at anytime, anywhere, anytime. Because of the limited signal transmitting power of the wireless access point (access Point APs). Its coverage is limited. Mobile terminal terminal MTT needs to switch between multiple APs. However, the large handoff delay will significantly affect the quality of real-time service such as VoIP. This paper focuses on MT cutting of large-scale deployed wireless WiFi networks when users are dense. The problem of service quality decline caused by exchange is studied. By introducing auxiliary nodes to co-scan the available channels, the handoff delay can be reduced. The main research work in this paper is as follows: 1) analyze the switching process of MT in MAC layer and the cause of delay. In this paper, the delay generation and improvement mechanism of the most time-consuming detection scanning phase is studied, and the MAC layer handoff method based on channel cooperative scanning technology is proposed and its flow is described. Before MT starts the switching process of MAC layer, the pre-scanning process which is triggered by the signal intensity threshold of AP is designed, aiming at the uncertainty of the available auxiliary scanning nodes in the actual scene. A distance first auxiliary node selection algorithm is proposed. At the same time, a selective parallel channel cooperative scanning algorithm is proposed to solve the problem of adjacent channel interference in the scanning process, which performs distributed detection at the same time. The AP information of the auxiliary node response is collected by using MT, which realizes the efficient collection of the switching auxiliary information. In order to further improve the switching speed of MT between historical APs, a scheme using the most recent AP list cache is proposed, which can effectively avoid repeated scanning times in short time intervals. A large number of mobile nodes are deployed through NS-2 simulation software, and the handoff in WiFi network is tested on the basis of introducing channel cooperative scanning algorithm. The experimental results show that. The proposed handoff scheme can effectively reduce the handoff delay and improve the quality of service for real-time applications such as VoIP video stream transmission and so on.
【學(xué)位授予單位】：長(zhǎng)安大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2016
【分類號(hào)】：TN92

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