一种新的用于IEEE 802.11e EDCA中提供QoS的方法

该文提出了一种新的应用于IEEE 802.11e EDCA (Enhanced Distributed Channel Access)中提供QoS(Quality of Service)的方法。这种方法是将几个时隙组合起来构成一个超时隙,每个超时隙的开始分配给不同的业务来进行发包。时隙的分配是根据各种业务的不同优先级来实现的。这种方法可以保证高优先级业务具有较大的吞吐量,较少的MAC延时和较低的丢包率。与802.11e EDCA草案中提出的不同冲突窗口大小的方法相比,这种方法具有可以提高吞吐量,降低丢包率,并能减小站点数目变化对高优先级业务吞吐量的影响等优点。这种新的提供QoS的方法优于不同冲突窗口大小的方法,在IEEE 802.11e EDCA中应用超时隙方法可以大大提高EDCA的性能。     

基于802.11e的无线多跳自适应合作式QoS算法

 为解决Ad hoc网络中转发节点拥塞和低优先级业务增多而影响高优先级业务带宽的问题,提出了一种无线多跳网络服务质量保证框架WMHQ(Wireless Multiple Hop QoS)和自适应合作式信道接入算法QAC-EDCA(QoS guaranteed Adaptive Cooperation EDCA).算法将802.11e的优先级区分机制扩展成了三层优先级机制,通过将业务的服务质量需求映射成时隙利用率进行周期性的监测,并以控制帧捎带的方式在两跳范围内传播竞争窗口调整信息,使得高优先级业务具备剥夺低优先级业务带宽的能力和拥塞节点具有协调获取更多带宽的能力.仿真表明,该算法相对802.11e能更好地保护多跳情况下高优先级业务的服务质量.     

基于M/G/1/K排队模型的IEEE802.11e EDCA性能研究

该文利用二维Markov链分析方法,提出了一种新的IEEE802.11e EDCA网络分析模型,该模型引入了空闲状态和不同接入等级的仲裁帧间隔(AIFS)的使用;利用Markov链状态转移图的Z域信号传递函数推导了MAC层平均服务时间的概率分布;结合M/G/1/K排队模型分析了增强分布式信道接入(EDCA)在非饱和和饱和负载下的性能。经过访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。分析结果表明:EDCA接入机制只为不同优先级业务提供QoS区分;不同优先级业务信道接入的不公平性是EDCA接入机制的特点。     

AdHoc多跳网络在EDCA机制下对实时音／视频业务的仿真分析

在AdHoc多跳网络中,IEEE802.11e协议采用了增强型分布信道接入机制（Enhanced Distributed Channel Access,EDCA）,用于为实时多媒体业务提供有效的QOS保证机制。本文简单介绍和对比了802.11分布式协调功能（DCF）和802.11e EDCA两种信道接入机制,并通过使用网络仿真软件OPNET,模拟了实时的视／音频业务在802.11DCF和802.11e EDCA信道接入机制下在不同网络负载下的性能并进行了仿真分析。     

车载自组织网络中基于邻居节点数估计的最小竞争窗口调整算法

针对基于IEEE 802.11p的车载自组织网络(VANET)中控制信道上周期性广播的可扩展性问题,提出了一种基于邻居节点估计的最小竞争窗口调整算法.首先,在IEEE 802.11广播退避的马尔可夫模型的基础上,以最小化碰撞概率为目的,推导出最小竞争窗口(CWmin)和活跃节点数n之间的关系;然后,利用周期性广播的beacon消息的特点对节点的邻居节点数进行实时估计,并根据估计的邻居节点数动态调整最小竞争窗口;最后,对提出的算法和IEEE 802.11p固定CWmin方法进行仿真比较分析.结果表明,提出的算法在广播接收率上优于原始方法.     

无线Mesh网络中支持QoS的802.11e协议优化

在无线Mesh网络中,支持QoS的IEEE 802.11eEDCA协议,其固定的队列接入机制,使得在网络负载较重的时高优先业务的QoS得不到应有的保障,同时在网络负载较轻时信道利用率也不高.文中提出了一种动态调整业务接入队列的算法.节点可以根据感知到的网络负载状况自适应调整队列接入方式,在保障高优先级业务QoS要求的同时,尽可能提高信道的利用率.仿真结果表明,在不同网络负载的场景下,该算法相对于IEEE802.11e在QoS保障和利用率方面都有较好的表现.     

IEEE802.11e EDCA和CFB下饱和吞吐量分析

IEEE802.11eMAC草案规范对IEEE802.11无线局域网标准在QOS方面加以了补充。IEEE802.11e采用2种协调机制基于控制的综合协调可控信道接入方式HCCA和基于竞争的增强型分布式信道接入方式EDCA。主要评估EDCA和竞争空闲脉冲(contention-freeburst)CFB相结合时,在系统负载过载的情况下,改变性能参数后系统饱和吞吐量的变化,并分析系统性能参数对饱和吞吐量的影响,从而达到系统参数优化的作用。     

基于创新扩散的多预约802.11e协议及性能分析

该文为Ad hoc网络媒质接入层提出了一种基于802.11e协议的支持区分服务支持的协议。该协议采取多预约机制提高高优先级数据业务在信道竞争中的优势,并且采用创新的扩散原理协调降低各个低优先级数据业务的接入概率,保护高优先级数据流,同时避免了这种协调信息在全网络范围内的洪泛。理论分析与仿真结果均表明,该扩展协议提高了高优先级数据流的接入概率和端到端吞吐量,显著的降低高等级业务的端到端时延及抖动。     

Ad hoc网络中一种生命周期约束的自适应退避算法

在IEEE 802.11标准定义的BEB退避算法基础上,提出一种生命周期约束的自适应退避算法LCAB,以生命周期代替最大重传次数作为分组丢弃的依据,并根据网络忙闲程度自适应地调整节点执行退避过程的权限,以最大化系统归一化有效吞吐量,适合于ad hoc网络中有严格时延要求的VoIP等实时性业务.构建Markov链模型分析LCAB算法性能,得到系统归一化有效吞吐量表达式.仿真结果表明,理论分析与仿真结果一致,且LCAB算法的归一化有效吞吐量优于BEB算法.     

移动Ad Hoc网络中一种分布式QoS保证的多址接入协议

基于随机竞争和冲突解决的思想,本文为多跳移动Ad Hoc网络提出了一种分布式服务质量(QoS)保证的多址接入(QMA)协议.该协议中,节点在发送业务分组前利用预报突发进行竞争接入,节点根据业务分组时延情况和最早失效优先原则确定预报突发的长度,所发预报突发能持续到最后的节点优先获得接入.同时,具有实时业务的节点可以按照其优先级在更早的竞争微时隙中开始发送预报突发,而有非实时业务的节点只能在前面竞争微时隙空闲的情况下,才能在后面的微时隙开始发送预报突发,因此发送实时业务的节点可以比发送非实时业务的节点更优先接入信道,从而在移动Ad Hoc网络中实现了对多媒体业务的QoS保证.最后利用OPNET仿真评估了QMA协议的多址性能,并与IEEE 802.11e协议的性能做了比较,结果表明QMA协议可以提供较高的吞吐量和较低的实时业务时延.     

Saturation Throughput Analysis of the IEEE 802.11e EDCA Network with Contention Free Burst Under Fading Channel

The 802.11 WLAN legacy standard cannot provide Quality of Service (QoS) support for multimedia applications because the 802.11 was initially developed for Best Effort services. Hence, the 802.11e amendment was published in order to provide the QoS support to WLANs. One of the most important functions in 802.11e is the contention based channel access mechanism called Enhanced Distributed Channel Access (EDCA), which provides a priority scheme by differentiating the Arbitration Inter Frame Space (AIFS), initial window size and Transmission OPportunity limit (TXOPlimit). In this paper, we propose a novel analytical model for the performance analysis of the IEEE 802.11e EDCA network with Contention Free Burst under fading channel and saturated traffic conditions. This new model captures all of the major QoS specific features, namely AIFS, minimum contention window size, maximum contention window size, virtual collision and TXOPlimit. So, we have analyzed the saturation system throughput of the basic access method of the IEEE 802.11e EDCA network.     

Impact of priority differentiation on the bridged WBAN/WLAN healthcare networks

In this work, we develop a prioritized bridging mechanism between the IEEE 802.15.6‐based wireless body area networks (WBANs) and the IEEE 802.11e enhanced distributed channel access (EDCA)‐based wireless local area network (WLAN) to convey the medical data to the medical center. We map the eight WBAN user priorities (UPs) into the four WLAN access categories (ACs) to provide the required quality of service and prioritization for the health variables generated by the WBAN nodes. By assignment of WBAN UPs with default medium access control parameters to eight different medical data streams and under the presence of ordinary nodes, we investigate the impact of WLAN AC differentiation by arbitrary inter‐frame space (AIFS) and contention window (CW) on performance of medical and regular nodes’ data streams. The results of this work indicate that the AC differentiation by AIFS outperforms the differentiation by CW in the sense that it does not deteriorate the end‐to‐end delay of relayed WBAN traffic and ordinary WLAN traffic.Copyright © 2012 John Wiley & Sons, Ltd.     

Supporting multimedia streaming and best‐effort data transmission over IEEE 802.11e EDCA

As demand for broadband multimedia wireless services increases, improving quality of service (QoS) of the widely deployed IEEE 802.11 wireless LAN (WLAN) has become crucial. To support the QoS required by a wide range of applications, the IEEE 802.11 working group has defined a new standard: IEEE 802.11e. In this paper, we propose a measurement‐based dynamic media time allocation (MBDMTA) scheme combined with a concatenating window scheme to support real‐time variable bit rate (rt‐VBR) video and best‐effort (BE) data transmission using IEEE 802.11e enhanced distributed channel access (EDCA). To provide the QoS guarantee for rt‐VBR video, the proposed MBDMTA scheme dynamically assigns channel time to the rt‐VBR video based on the estimate of the required network resources. On the other hand, the concatenating window scheme controls the contention window (CW) ranges of different priority flows such that real‐time services always have higher channel access probability, thus achieving the capability of preemptive priorities. In addition, the concatenating window scheme preserves fairness among flows of the same class and attains high channel utilization under different network conditions. Simulation results demonstrate that the throughput and delay performance improve significantly for the transmission of rt‐VBR video and BE traffic as compared to those for the 802.11e EDCA specification. It is also revealed that combining the two proposed schemes provides seamless integration and reliable transmission of digital video and data service within the 802.11e EDCA framework. Copyright © 2007 John Wiley & Sons, Ltd.     

Incomplete cooperation‐based service differentiation in WLANs

In the IEEE 802.11 wireless LAN (WLAN), the fundamental medium access control (MAC) mechanism—distributed coordination function (DCF), only supports best‐effort service, and is unaware of the quality‐of‐service (QoS). IEEE 802.11e enhanced distributed channel access (EDCA) supports service differentiation by differentiating contention parameters. This may introduce the problem of non‐cooperative service differentiation. Hence, an incompletely cooperative EDCA (IC‐EDCA) is proposed in this paper to solve the problem. In IC‐EDCA, each node that is cooperative a priori adjusts its contention parameters (e.g., the contention window (CW)) adaptively to the estimated system state (e.g., the number of competing nodes of each service priority). To implement IC‐EDCA in current WLAN nodes, a frame‐analytic estimation algorithm is presented. Moreover, an analytical model is proposed to analyze the performance of IC‐EDCA under saturation cases. Extensive simulations are also carried out to compare the performances of DCF, EDCA, incompletely cooperative game, and IC‐EDCA, and to evaluate the accuracy of the proposed performance model. The simulation results show that IC‐EDCA performs better than DCF, EDCA, and incompletely cooperative game in terms of system throughput or QoS, and that the proposed analytical model is valid. Copyright © 2010 John Wiley & Sons, Ltd.     

Performance analysis of IEEE 802.11e contention-based channel access

The new standard IEEE 802.11e is specified to support quality-of-service in wireless local area networks. A comprehensive study of the performance of enhanced distributed channel access (EDCA), the fundamental medium access control mechanism in IEEE 802.11e, is reported in this paper. We present our development of an analytical model, in which most new features of the EDCA such as virtual collision, different arbitration interframe space (AIFS), and different contention window are taken into account. Based on the model, we analyze the throughput performance of differentiated service traffic and propose a recursive method capable of calculating the mean access delay. Service differentiation functionality and effectiveness of the EDCA are investigated through extensive numerical and simulation results. The model and the analysis provide an in-depth understanding and insights into the protocol and the effects of different parameters on the performance.     

Saturation Throughput Analysis of IEEE 802.11e EDCA Through Analytical Model

The IEEE 802.11e EDCA is designed to provide quality of support for real time applications with stringent latency and throughput requirements. Theoretical frameworks for analysis of throughput performance of wireless LAN employing exponential back-off exist extensively. Several models rely on simplification assumptions that preclude their direct applicability to the enhanced distributed coordination access (EDCA) which uses heterogeneous protocol parameters, while other models are exceedingly complex to analyze. In this paper, a tractable analytical model is proposed for saturation throughput of the IEEE 802.11e EDCA. The prioritization through channel access parameters including the AIFS and contention window is catered for within a three dimensional Markov chain. The integration of back-off counter freezing and retry limit enhance the models precision. Its validation is done by simulation on NS-2. Practical applicability of the model is established based on accuracy and computational efficiency. The model is utilized for throughput analysis of the EDCA under saturated traffic loads.     

A fuzzy logic cooperative MAC for MANET

In both wireless local area networks（WLAN） and mobile ad hoc networks（MANET）, the 1EEE 802.11e medium access control （MAC） protocol is proposed for an effective quality of service （QoS） solution. A number of studies have been done to enhance the performance of 802.11e in MANET by independently adjusting contention window （CW） size of each access category （AC） in every node. However, without the cooperation between the high priority flows and lower priority flows, the QoS goal of high priority flows cannot achieve effectively. In this article, a fuzzy logic based cooperative MAC protocol （FLCMAC） is proposed to cooperate amongst network flows and dynamically adjust access probability of each low priority flow affecting the high priority flows to satisfy their QoS requirement. The simulation results indicate that compared to the enhanced distributed channel access （EDCA） scheme of 802.11e, the FLCMAC consistently excels, in terms of throughput and delay under moderate and heavy background traffic both in single-hop and multi-hop scenarios.     

Stable operation of IEEE 802.11e EDCA: Interaction between offered load and MAC parameters

In this paper, we study impacts of TXOP allocation and AIFS parameter on one hop IEEE 802.11e EDCA network under varying offered load. Offered load is modified by changing the parameters of arrival process and node populations. Arrival process is varied by altering burst size distribution, mean burst size, frame size, and arrival rates. We investigate the effects of the offered load parameters on the network stability and non-saturation boundaries of IEEE 802.11e EDCA. Our results show interaction of offered load and MAC parameters. The results suggest the range of network parameters which preserve network stability and still achieve QoS differentiation.     

A MAC-Layer QoS Provisioning Protocol for Cognitive Radio Networks

Due to the proliferation of diverse network devices with multimedia capabilities, there is an increasing need for Quality of Service (QoS) provisioning in wireless networks. The MAC layer protocol with enhanced distributed channel access (EDCA) in the IEEE 802.11-2007 is able to provide differentiated QoS for different traffic types in wireless networks through varying the Arbitration Inter-Frame Spaces (AIFS) and contention window sizes. However, the performance of high priority traffic can be seriously degraded in the presence of strong noise over the wireless channels. Schemes utilizing adaptive modulation and coding (AMC) technique have also been proposed for the provisioning of QoS. They can provide limited protection in the presence of noise but are ineffective in a high noise scenario. Although multiple non-overlapped channels exist in the 2.4 and 5?GHz spectrum, most IEEE 802.11-based multi-hop ad hoc networks today use only a single channel at anytime. As a result, these networks cannot fully exploit the aggregate bandwidth available in the radio spectrum provisioned by the standards. By identifying vacant channels through the use of cognitive radios technique, the noise problem can be mitigated by distributing network traffic across multiple vacant channels to reduce the node density per transmission channel. In this paper, we propose the MAC-Layer QoS Provisioning Protocol (MQPP) for 802.11-based cognitive radio networks (CRNs) which combines adaptive modulation and coding with dynamic spectrum access. Simulation results demonstrate that MQPP can achieve better performance in terms of lower delay and higher throughput.     

Efficient Back-off Mechanism for Multimedia Support in 802.11e EDCA Wireless Ad-Hoc Networks

This paper presents an effective back-off mechanism to improve quality of service (QoS) for multimedia applications over the IEEE 802.11e enhanced distribution channel access (EDCA) standard. It can be done with proposed algorithm called dynamic fast adaptation for contention-based EDCA (DFA-EDCA) mechanism. The main concept of proposed DFA-EDCA mechanism is to use the exponential functions to adaptively tune the back-off parameters in IEEE 802.11e EDCA according to the changes on a network load within a short period. In this proposed mechanism an intra-access category (intra-AC) differentiation mechanism is provided to increase its back-off time randomly and achieve discrimination of same priority traffic on different stations. The performance evaluations have been conducted by using Network Simulator (NS-2). The simulation results show that the proposed DFA-EDCA mechanism has greatly outperformed the previous mechanisms such as non-linear dynamic adaptation scheme of the minimum contention window (CW_min-HA), dynamic adaptation algorithm of the maximum contention window (CW_max-adaptation), adaptive enhanced distributed coordination function and the conventional EDCA in terms of goodput, gain of goodput, packet delay, collision rate and channel utilization ratio (CUR). It has significantly reduced both packet delay and collision rate simultaneously together with an obviously increment in both goodput and CUR, which lead to the improvement in QoS for multimedia applications.