IEEE 802.11e EDCA在Ad Hoc网络中应用仿真分析

IEEE 802.11e EDCA协议通过采用MAC层业务区分的方式,提供网络的QoS支持.分析并比较了802.11e EDCA对802.11 DCF的改进,并通过NS2仿真分析EDCA在Ad Hoc网络中的应用情况,进一步讨论并仿真实现了对EDCA协议参数的分析.仿真结果表明,EDCA在多跳Ad Hoc网络中仍保持了其有效性,实现业务区分并提高了网络的吞吐量等性能,同时协议参数的不同将极大的影响系统性能,通过优化设置参数可以进一步提高系统性能.     

WLAN基于竞争的信道接入机制分析研究

在文中,首先介绍了IEEE802.11 MAC层采用的DCF接入机制,然后介绍了IEEE802.11e MAC层采用的EDCA机制。对比分析DCF和EDCA接入机制,指出优点和不足,提出了下一步的研究方向。     

IEEE 802.11p车载自组网络协议的EDCA自适应退避算法研究

IEEE 802.11p是IEEE针对车辆网络颁布的物理层与MAC层标准,网络中车辆密度是动态变化的,而IEEE 802.11p协议没有提出根据网络情况动态调整EDCA参数来优化网络性能。为了解决网络中节点密度变化带来的吞吐量低、碰撞率高的问题,提出一种EDCA自适应退避优化算法。仿真实验结果表明,该算法相对于传统EDCA算法,性能大幅度提高。     

饱和状态下IEEE 802.11e EDCA机制的建模分析

建立了一个合适的IEEE 802.11e EDCA信道接入机制的数学分析模型。首先深入研究了IEEE 802.11e EDCA机制;在此基础上提出了一种新型的饱和状态下EDCA分析模型。该模型采用二维Markov链的分析方法,分别考虑了不同业务在进行退避时,检测到信道忙的概率以及不同业务退避到零,发送数据帧时发生冲突的概率在多业务竞争中产生的影响。进一步地,对该模型进行了延迟分析。数学分析和仿真实验的对比表明,该模型能够很好地描述IEEE 802.11e EDCA信道接入机制的MAC接入延迟。     

WLAN中基于EDCA机制的接纳控制研究

分析IEEE802.11e的服务质量（QoS）调度机制和EDCA访问机制,基于保证通信服务质量、改良EDCA参数,适合分布式的ad hoc网络的运用,提出了一种接纳控制方案和EDCA参数调节改良机制,有效提高了媒体接入控制。     

基于EDCA的SVC视频传输的跨层动态映射算法

通过对H.264/SVC可分级视频编码技术和IEEE 802.11e的EDCA协议的研究,提出了基于可分级视频的动态跨层映射算法。该算法综合考虑了可分级视频的分组的重要性和MAC层EDCA协议的优先级队列的映射机制,通过应用层发起MAC层响应的跨层联合优化的方式,将视频分组动态的映射到MAC层中合适的队列中。通过采用网络仿真工具NS2进行仿真,对比EDCA机制、跨层静态映射算法和跨层动态映射算法,仿真结果表明跨层动态映射算法能够明显提高视频传输的服务质量。     

RTS/CTS对802.11e在多跳无线网络中的影响

IEEE802.11e的增强分布式信道接入机制(EDCA)对业务的服务质量提供支持,由于其增强高优先级信道竞争能力而提供服务区分的主要特点而应用于Ad Hoc网络中.本文探讨了802.11e应用于多跳无线网络在不同的侦听范围下RTS/CTS有效性问题,指出:网络仿真工具NS2中对于节点传输范围和侦听范围的默认设置使得MAC层使用了RTS/CTS后网络性能变差.通过理论分析,并对不同侦听范围、跳数增加、TCP最大窗口的减小在有无RTS/CTS时的不同性能表现进行仿真分析,最终确定结论的正确性.     

IEEE 802.11e EDCA机制的一种参数调节策略

研究了IEEE 802.11e EDCA机制的原理和无线信道利用模型,阐明了EDCA参数设置对其性能的重要性。在此基础上,提出了一种简单有效的参数调节策略。仿真结果表明,该参数调节机制在保证实时业务要求的同时,可以显著提高数据流的吞吐率,优化了EDCA机制的运行性能。     

存在隐藏终端的IEEE802.11e多跳无线网络模型分析

首次将802.11e的接入机制放入多跳环境中进行仿真分析和定量研究。提出一种新的多跳环境下802.11e网络模型,结合M/G/1/K排队模型,定量分析在隐藏终端影响下802.11e网络的MAC层吞吐率、MAC时延和帧丢失率,研究802.11e在多跳环境下性能表现的内在原因。经过仿真实验结果与数值分析结果的对比,验证了分析模型的准确性;通过有(无)隐藏终端影响下MAC层性能的对比分析,指出了802.11e在多跳无线网络中支持QoS的局限性:受隐藏终端的影响,802.11e对不同接入等级的业务提供QoS区分的性能明显降级。因而有必要研究隐藏终端问题的解决方案,提高802.11e在多跳环境下的性能。     

存在隐藏终端的IEEE 802.11e多跳无线网络模型分析*

首次将802.11e的接入机制放入多跳环境中进行仿真分析和定量研究。提出一种新的多跳环境下802.11e网络模型,结合M/G/1/K排队模型,定量分析在隐藏终端影响下802.11e网络的MAC层吞吐率、MAC时延和帧丢失率,研究802.11e在多跳环境下性能表现的内在原因。经过仿真实验结果与数值分析结果的对比,验证了分析模型的准确性;通过有（无）隐藏终端影响下MAC层性能的对比分析,指出了802.11e在多跳无线网络中支持QoS的局限性：受隐藏终端的影响,802.11e对不同接入等级的业务提供QoS区分的性能明显降级。因而有必要研究隐藏终端问题的解决方案,提高802.11e在多跳环境下的性能。     

IEEE802.11e中基于无确认策略的EDCA机制研究

本文分析了IEEE802．11中DCF和IEEE802．11e中EDCA两种信道接入机制，研究了无确认策略在两种机制下对语音等实时业务QoS的支持能力。通过opnet软件仿真得出，相比于DCF，基于无确认策略的EDCA机制提高了实时业务的QOS，对当前WLAN网络中实时业务的传输有着重要的指导意义。     

Saturated throughput analysis of IEEE 802.11e EDCA

IEEE 802.11e standard has been published to introduce quality of service (QoS) support to the conventional IEEE 802.11 wireless local area network (WLAN). Enhanced distributed channel access (EDCA) is used as the fundamental access mechanism for the medium access control (MAC) layer in IEEE 802.11e. In this paper, a novel Markov chain based model with a simple architecture for EDCA performance analysis under the saturated traffic load is proposed. Compared with the existing analytical models of EDCA, the proposed model incorporates more features of EDCA into the analysis. Firstly, we analyze the effect of using different arbitration interframe spaces (AIFSs) on the performance of EDCA. That is, the time interval from the end of the busy channel can be classified into different contention zones based on the different AIFSs used by different sets of stations, and these different sets of stations may have different transmission probabilities in the same contention zone. Secondly, we analyze the possibility that a station’s backoff procedure may be suspended due to transmission from other stations. We consider that the contention zone specific transmission probability caused by the use of different AIFSs can affect the occurrence and the duration of the backoff suspension procedure. Based on the proposed model, saturated throughput of EDCA is analyzed. Simulation study is performed, which demonstrates that the proposed model has better accuracy than those in the literature.     

A simple recursive scheme for adjusting the contention window size in IEEE 802.11e wireless ad hoc networks

The IEEE 802.11e standard has been introduced recently for providing Quality of Service (QoS) capabilities in the emerging wireless local area networks. This standard introduces a contention window based Enhanced Distributed Channel Access (EDCA) technique that provides a prioritized traffic to guarantee the minimum bandwidth needed for time critical applications. However, the EDCA technique resets the Contention Window (CW) of the mobile station statically after each successful transmission. This static behavior does not adapt to the network state since it reduces the network usage and results in bad performance and poor link utilization whenever the demand for link utilization increases. This paper proposes a new adaptive differentiation technique for IEEE 802.11e Wireless Local Area Networks that takes into account the network state before resetting the contention window. In the new technique, the congestion level of the network is sensed by using previous CW values. Three other enhancement techniques that focus on network adaptation are also discussed. Their main limitations are the high complexity of the implemented algorithms and their slow adaptation to the network state when the channel experiences bursty traffic. The proposed technique is compared to the original differentiation techniques of IEEE 802.11a and IEEE 802.11e standards, as well as to the enhancement schemes. Results show that the proposed adaptive technique outperforms IEEE 802.11e and is comparable to the other enhancement schemes while maintaining relatively low complexity requirements.     

速率自适应的无线Mesh 网拥塞控制

在IEEE 802.11s 标准草案基础上,结合TCP 协议中的AIMD算法,提出一种针对无线Mesh 网的速率自适应拥塞控制策略。该策略与IEEE 802.11e EDCA相比,在有效缓解网络拥塞的同时,保证了高优先级业务与低优先级业务之间的公平性。试验结果表明该拥塞控制策略是有效可行的。     

Extended EDCA for delay guarantees in wireless local area networks

Despite their very broad diffusion, IEEE 802.11 Wireless Local Area Networks (WLANs) are not able to provide service differentiation and to support real-time multimedia applications, due to their channel access methods. To overcome these limitations, the 802.11e working group has proposed the Enhanced Distributed Coordination Access (EDCA) scheme, which achieves service differentiation on a statistical basis by properly mapping user Quality of Service (QoS) requirements to channel contention parameters. Such a scheme will be included in the emerging 802.11n standard and in the revision of the 802.11 standard. However, it has been widely demonstrated that, especially at high network loads, EDCA does not provide an effective usage of the channel capacity. In particular, it is unable to provide a bounded delay service to all kinds of multimedia flow because flows with lower channel access priorities are starved to advantage only those with the highest priority. To fix this undesired behavior and improve wireless LAN performance, this paper proposes a new Extended EDCA (E²DCA) scheme, that is compliant with 802.11e specifications. By exploiting a closed-loop control algorithm, E²DCA performs a distributed dynamic bandwidth allocation, providing guarantees on average/absolute delays to real-time media flows, regardless of their priorities. Moreover, an innovative Call Admission Control (CAC) procedure has been developed. Using the ns-2 simulator, the effectiveness of the algorithm has been investigated in realistic network scenarios, involving a mix of audio, video, and FTP flows, at several network loads and with random losses. Results have shown that the proposed scheme is able to provide a bounded delay service to multimedia flows in a wide range of network loads and frame loss ratios.     

支持QoS的IEEE 802.11 EDCA性能研究

随着无线网络应用的不断发展,为了适应网络中不同类型业务的区分服务需要,IEEE 802.11工作组在IEEE 802.11 DCF(distributed coordination function)的基础上推出了支持QoS的IEEE 802.11 EDCA协议.针对EDCA(enhanced distributed channel access)协议的优先级区分信道接入特性,提出了一种基于Markov链的协议性能模型分析方法.与已有文献不同,该模型分析同时包含了EDCA主要的3个关键区分信道接入机制:Wmin/Wmax,AIFS(arbitration inter-frame space),TXOP(transmission opportunity).通过模型分析,获得了EDCA协议各优先级接入的传输吞吐量、信道接入延迟、数据丢失率等性能分析.不仅分析了饱和情形下的EDCA性能,而且还对非饱和情形下的EDCA性能进行了分析.仿真验证结果表明,模型分析结果和仿真结果取得了很好的一致性.利用给出的模型分析方法,提出了一种基于TXOP动态调整的D-TXOP(dynamic TXOP)接纳控制算法.算法根据网络中业务流的QoS要求,在动态调整各优先级的TXOP参数设置的基础上,对网络中新到业务流进行接纳控制,达到提高网络的业务承载能力的目的.