WLAN QoS支持机制-IEEE 802.11e

介绍了为WLANs提供业务质量(QoS)支持机制的IEEE802.11e标准草案。通过与802.11标准的MAC层进行对照分析,指出了802.11e草案对MAC层所作的改进。着重分析了改进的分布协调功能与混合协调功能两种新的QoS支持机制。     

IEEE802．11eWLAN中基于HCCA机制的带宽分配算法的研究

随着使用WLAN（无线局域网）接入因特网的日渐普及,IEEE802．11eWLAN中的HCCA（混合控制信道接入）机制由于在处理实时多媒体业务的高效率受到越来越广泛的关注。在WLAN中为达到高带宽利用率和良好的端到端QoS,介绍了一种基于HCCA机制的带宽分配算法,同时对该算法与802．11PCF（点协调功能）两种接入场景下的网络性能进行仿真比较,其结果验证了该算法可以为WLAN提供良好的QoS保证,对在WLAN中传输语音、视频等实时业务具有一定的指导意义。     

基于IEEE802.11e HCCA的接入控制方案

较传统的IEEE802.11标准的MAC协议,802.11e增强了对QoS的支持力度,主要基于IEEE802.11e的HCCA机制,提出了一套控制接入方案,本方案在全面考虑QoS参数的基础上提出了一个有效的调度算法,从而确保了实时性业务的QoS需要.     

基于动态优先级表的TDMA时隙分配

Ad Hoc网络组网效率提升的一个重要方面就是研究高效的时隙分配算法,动态TDMA时隙分配机制已经成为提高组网效率的一个热门研究点。这里基于动态优先级表提出一种新颖的动态时隙分配算法,该算法能在时间维上保证各节点对空闲时隙资源竞争使用的公平性。仿真结果表明基于动态优先级表的时隙分配算法能高效利用时隙资源,提高信道利用率。     

MAC Layer Admission Control and Priority Re-allocation for Handling QoS Guarantees in Non-cooperative Wireless LANs

Providing QoS guarantee with appropriate service differentiation in IEEE 802.11 wireless LANs is quite desirable. However, users may be selfish and thus rigorously try to maximize their performance by demanding high services even though the network has already saturated. On the other hand, user misbehaviors such as misuse of priority and over-rate transmission pose further harm to performance of existing flows. These application layer non-cooperation makes successful resource allocation very challenging with existing contention based CSMA/CA channel access. In this paper, we propose a MAC layer coordinated QoS framework of admission control and priority re-allocation for quality of services of real-time applications in wireless LANs. Our focus is on priority based MAC schedulers where each user can set its flow priority in order to receive appropriate level of services. With channel condition information such as available bandwidth and mean delay exchanged among neighboring stations, users can enforce admission control based on the perceived channel status and may re-allocate their priorities to accommodate existing flows as desired. User misbehaviors are identified by estimating the flow transmitting rate and matching priority setting, or even punished by assigning appropriate low priorities. Extensive simulations results show that the proposed framework can effectively coordinate wireless users on keeping reserved transmission rate, using appropriate MAC priority, and allocating sufficient resource. Ming Li received his B.S. and M.S. in Engineering from Shanghai Jiao Tong University, China, in 1995 and 1998, respectively. He is currently a Ph.D. candidate in department of Computer Science, University of Texas at Dallas, where he received M.S. degree in Computer Science in Dec. 2001. His research interest includes QoS schemes for mobile ad-hoc networks and multimedia over wireless networks. B. Prabhakaran is with the faculty of Computer Science Department, University of Texas at Dallas. He has been working in the area of multimedia systems: animation & multimedia databases, authoring & presentation, resource management, and scalable web-based multimedia presentation servers. Dr. Prabhakaran received the prestigious National Science Foundation (NSF) CAREER Award in 2003 for his proposal on Animation Databases. He has published several research papers in various refereed conferences and journals in this area. He has served as guest-editor (special issue on Multimedia Authoring and Presentation) for ACM Multimedia Systems journal. He is also serving on the editorial board of Multimedia Tools and Applications journal, Kluwer Academic Publishers. He has also served as program committee member on several multimedia conferences and workshops. B. Prabhakaran has served as a visiting research faculty with the Department of Computer Science, University of Maryland, College Park. He also served as a faculty in the Department of Computer Science, National University of Singapore as well as in the Indian Institute of Technology, Madras, India.     

A Generalized Saturation Throughput Analysis for IEEE 802.11e Contention-Based MAC

The main service differentiation mechanism introduced by the IEEE 802.11e standard is described in terms of prioritized contention access. Analyzing the performance and service differentiation ability of each of the priority features of the 802.11e standard is an important task, and considerable research effort has recently been dedicated to this subject. In this article, we present a generalized and comprehensive analysis of the prioritized access scheme of the 802.11e standard. Our model corrects and extends the existing models and considers all priority features of the 802.11e Medium Access Control (MAC) protocol. We consider an arbitrary number of priority levels, and provide a detailed parametric analysis of the MAC behavior for the main priority parameters of inter frame spacing, contention window size, and transmission opportunity. We validate the accuracy of our analysis with simulation experiments.

基于802.11e的无线Mesh网络中视频传输优化方案

针对无线Mesh网络环境下视频数据传输的延迟、吞吐量、丢包率等问题,改进了一种数据映射方案,将不同重要程度的数据与IEEE 802.11e中的接入类别相对应,优先发送级别高的数据。对压缩视频数据传输进行了仿真实验,并对仿真结果进行了分析,证明了在不同的网络业务负载下,改进的映射方案对网络性能有一定的改善。     

一种可提供QoS保障的新型交换结构

本文采用带缓存交叉开关作为核心交换单元,构建了一种空分复用扩展的联合输入/交叉节点/输出排队(SDM-CICOQ)交换结构,从理论上证明了当扩展因子为2时,SDM-CICOQ交换结构可以获得100%的吞吐量,并且能够完全模拟输出排队(OQ)交换结构,从而能够提供服务质量(QoS)保障.本文还给出了一种层次化优先级调度(HPS)方案作为SDM-CICOQ交换结构调度机制的工程设计参考,仿真结果表明采用HPS调度方案SDM-CICOQ交换结构可获得良好的性能.     

Dynamic adaptation policies to improve quality of service of real-time multimedia applications in IEEE 802.11e WLAN Networks

With the increased popularity of wireless broadband networks and the growing demand for multimedia applications, such as streaming video and teleconferencing, there is a need to support diverse multimedia services over the wireless medium. In order to efficiently address these diverse needs, efforts have been pursued to provide Quality of Service (QoS) mechanisms for medium access, resulting in a standard called IEEE 802.11e. One of the enhancements proposed in IEEE 802.11e is a polling-based access mechanism, which is targeted for real-time multimedia flows. In this polling-based scheme, scheduling and time allocation are based on flow reservations. Hence, the effectiveness of the mechanism is heavily dependent on the accuracy of the flow requirements in the reservation. Flow requirements, however, can vary over time and an allocation based on fixed reservations cannot address this variability. This limitation, which is present in the reference scheduler of IEEE 802.11e, leads to degraded multimedia quality for flows with variable requirements, even when channel resources are available. In order to address the above limitation, we present an adaptation framework that dynamically adjusts the polling-based access mechanism and associates flows to different modes of access (polling-based/contention-based), according to the current needs of the application, as opposed to solely relying on the reservation parameters. We demonstrate that with our adaptation, the achieved QoS for real-time multimedia streams, in terms of delay and throughput metrics, can be significantly improved compared to other known mechanisms. Additionally, we show the benefits of our adaptation framework on overall multimedia quality and system capacity. This research is supported by the University of California Discovery Grant (com02-10123) and the Center for Wireless Communications (CWC), University of California, San Diego.     

On delay constrained CAC scheme and scheduling policy for CBR traffic in IEEE 802.11e wireless LANs

CBR (constant bit rate) traffic is expected to be an important traffic source in wireless networks. Such sources usually have stringent jitter or delay requirements and in many cases they should be delivered exactly as they were generated. In this paper, we propose a strictly guaranteed QoS (quality‐of‐service) provisioning CAC (call admission control) scheme with a polling‐based scheduling policy for CBR traffic in IEEE 802.11e wireless LANs. Under such a scheme, the proposed transmit‐permission policy for HCCA (HCF controlled channel access) method can forecast the maximum suffered delay for each packet and derive sufficient conditions so that all the CBR sources satisfy their time constraints to provide deterministic QoS guarantees. A simple analytical model is carried out to estimate the average queueing delay of the proposed scheme. In addition to theoretical analysis, simulations are conducted to validate its promising performance. Our simulation results show that the proposed scheme maintains a high throughput with respect to the whole range of system load. Copyright © 2009 John Wiley & Sons, Ltd.     

A Throughput and Delay Model for IEEE 802.11e EDCA Under Non Saturation

In this paper, we present a model to analyze the throughput and delay performance of the EDCA mechanism under non saturation conditions. The main strength of our model is that it can be used to analyze generic source models, as it neither makes any assumption on the source’s arrival process nor requires all packets be of the same length. Simulation results confirm the accuracy of our model under a variety of realistic source models, including (i) typical arrival processes for voice, video, and data traffic, and (ii) packet length distributions derived from measurements.     

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。     

Selectivity function scheduler for IEEE 802.11e HCCA access mode

In this paper, we present a scheduling algorithm that enhances the performance of the standard IEEE 802.11e scheduler for the Hybrid Coordination Function Controlled Channel Access mode. The main contribution in designing the proposed scheduler is the ability to accommodate multiple streams with different levels of Quality of Service requirements concurrently running on the same station. This is achieved by dynamically calculating the Transmission Opportunities of each active traffic stream (TS) and the appropriate Service Interval of each active station. The proposed algorithm optimizes the utilization of the scarce bandwidth resources by only polling active stations. The algorithm incorporates a selectivity function to assign polling priorities to the active streams only based on their diverse requirements and their link‐attainable transmission rates. The performance of the proposed Selectivity Function Scheduler (SFS) scheme is evaluated against the standard scheduler. Simulation results show that the SFS outperforms the standard scheduler in terms of enhancing streams' throughput, reducing packet dropping ratio and maintaining high fairness amongst the admitted TS. Copyright © 2011 John Wiley & Sons, Ltd.     

IEEE 802.11a无线局域网系统中的雷达信号检测方法

为了与5 GHz频段内的雷达系统共存,IEEE 802.11a无线局域网系统必须采用动态频率选择机制。当检测到有使用相同无线信道的雷达系统存在时,可根据需要转换到其他信道。文中对雷达信号的特征及现有的雷达信号检测方法进行了总结,并给出了其他候选的雷达信号检测方法。通过对各种方法的分析比较,给出了一种基于功率检测的雷达信号检测方法,该方法易于实现且具有较好的性能。     

Performance analysis of differentiated QoS in IEEE 802.11e WLANs

This paper proposes a multi‐dimensional Markov model to analyse the performance of the IEEE 802.11e EDCF MAC protocol. Based on this model, we present extensive performance evaluation in terms of throughput, throughput ratios, and access delay of flows of distinct priorities under RTS/CTS mode. We also provide quantitative analysis of the impact of prioritized parameters, i.e. Arbitration InterFrame Space (AIFS), Contention Window (CW) on Quality of Service (QoS) differentiation. The accuracy of the proposed model is verified by means of comparing the numerical results obtained from both analytical model and simulations. Our research can be used as a guideline for the prediction of how flows belonging to a certain Traffic Category (TC) perform with their TC‐specific parameters, as well as designing EDCF‐based WLANs and tuning the parameters to achieve the desirable differentiated QoS objectives. Copyright © 2005 John Wiley & Sons, Ltd.     

Proportional fair throughput allocation in multirate IEEE 802.11e wireless LANs

Under heterogeneous radio conditions, Wireless LAN stations may use different modulation schemes, leading to a heterogeneity of bit rates. In such a situation, 802.11 DCF allocates the same throughput to all stations independently of their transmitting bit rate; as a result, the channel is used by low bit rate stations most of the time, and efficiency is low. In this paper, we propose a more efficient throughput allocation criterion based on proportional fairness. We find out that, in a proportional fair allocation, the same share of channel time is given to high and low bit rate stations, and, as a result, high bit rate stations obtain more throughput. We propose two schemes of the upcoming 802.11e standard to achieve this allocation, and compare their delay and throughput performance. Albert Banchs received his M.Sc. and Ph.D. degrees in Telecommunications from the Technical University of Catalonia in 1997 and 2002, respectively. His Ph.D. received the national award for best thesis on Broadband Networks granted by the Professional Association of Telecommunication Engineers. He worked for the International Computer Science Institute, Berkeley, in 1997, for Telefonica I+D, Madrid, in 1998 and for NEC Network Laboratories, Heidelberg, from 1998 to 2003. Since 2003 he is with the University Carlos III of Madrid. Dr. Banchs is Associate Editor of IEEE Communications Letters and has been TPC member of several conferences and workshops including INFOCOM, ICC, GLOBECOM and QoS-IP. His current research interests include resource allocation, QoS and performance evaluation of wireless and wired networks. Pablo Serrano was born in Tarifa, Spain, on May 17, 1979. He received a M.Sc. degree in Telecommunications from the University Carlos III of Madrid in 2002. Since that date he is a Ph.D. candidate and a lecturer at the Telematics Department of the same university. His current research interests are performance evaluation and resource allocation of WLAN networks. Huw Edward Oliver received his MA degree in Mathematics at Cambridge University (1980), and his MSc (1985) and PhD (1988) in Computer Science at the University College of Wales, Aberystwyth. He joined Hewlett-Packard Laboratories, Bristol in 1989 to work on Software Development Environments. Following a period at HP’s Software Engineering Systems, Colorado in 1992 he returned to HP Labs in 1993 as Senior Member of Technical Staff and worked on real-time fault tolerant telecommunication systems. From 1997 to 2000 he was appointed Manager of Hewlett-Packard’s Internet Research Institute. He worked as Technical Director of the European MMAPPS Project from 2000 to 2002, as Senior Research Fellow at Lancaster University from 2002 to 2004, and as Visiting Professor at University Carlos III of Madrid from 2004 to 2005. Since 2005 he has been Senior Researcher with Ericsson R&D Ireland, Athlone where he is responsible for the next-generation network management architecture.     

无线ATM局域网中一种面向QoS的动态信道分配方案

提出了在无线ATM(异步传送模式)局域网中面向QoS(服务质量)的一种集中式DCA(动态信道分配)方案。此方案主要是在无线ATM局域网中,考虑了基站的相互干扰限制、目前信道资源利用以及有效连接的QoS保证等因素。仿真结果表明这种方案的系统性能获得了提高。     

Dynamic bandwidth partition schemes for integrated voice,video, and data traffic in the IEEE 802.11e distributed wireless LANs

In mobile cellular networks, bandwidth is deterministic in terms of the number of channels by frequency division, time division, or code division. On the other hand, bandwidth partition schemes in the contention‐based medium access control (MAC) in distributed wireless LANs are extremely challenging due to the contention‐based nature, packet‐based network, and the most important aspect: only one channel available, competed by an unknown number of stations. In this paper, we study this challenging issue. We propose and study four different bandwidth partition schemes for integrated voice/video/data traffic in the IEEE 802.11e wireless LANs: a Static bandwidth Partition (SP) scheme, a Dynamic budget Partition (DP) scheme, a Dynamic bandwidth Partition with Finer‐Tune (DP‐FT) scheme, and a Dynamic bandwidth Partition with Reserved Region (DP‐RR). The proposed schemes are compared and evaluated via extensive simulations. Results show that the DP‐FT scheme is the best scheme. Copyright © 2009 John Wiley & Sons, Ltd.     

IEEE 802_11e EDCF饱和状态下性能分析

IEEE 802．11e协议草案以增强型分布式协调功能（EDCF）为基础。用于加强对无线局域网标准IEEE 802.11的QoS支持力度。文章简要介绍了802．11中的分布式协调功能（DCF）和点怫调功能（PCF）。重点阐述了802.11e EDCF的基本原理和组成结构。使用网络模拟工具NS-2对比了DCF和EDCF的吞吐量，并对EDCF在饱和状态下以及站点慢速移动情况下的性能进行了详细的分析和比较。