无线局域网MAC层QoS研究

在分析无线网协议提供QoS保证方面存在的问题的基础上，讨论了IEEE802．11e的两个新的策略：增强的分布式协调功能和混合协调功能。通过对受控竞争机制的分析．指出了IEEE802．11e仍存在的不足及未来的发展方向。     

WLAN接入控制技术

WLAN因其应用日益广泛而备受关注。作为未来核心网的一种重要的接入形式，WLAN需要满足现在和未来网络对高服务质量的要求和多样化的要求，高质量要求做好底层传输和设计合适的接入控制协议，多样化要求在对用户的接入控制的优先级和资源分配上结合用户的服务质量要求。本文概述了WLAN的接入控制，描述了结合服务质量的接入控制思想，分析了现有技术存在的问题，提出了以后的改进方向。     

一种增强MANET网络QoS性能的MAC机制

采用一种增强MANET网络QoS性能的MAC机制,引用“接力传输”和“接力中断”两种新的操作方法。对高优先级业务,MAC帧由源端被“接力”传输至目的端;对不同优先级的业务,产生不同次数的“接力中断”。每次接力中断增加一次信道竞争,由此达到不同优先级业务的区分。NS-2仿真表明此机制的有效性。     

基于网络感知的可用带宽评估机制研究

提出了一种基于IEEE802.11的Ad Hoc网络改进的可用带宽评估机制,该评估机制考虑了帧同步和碰撞概率对链路可用带宽的影响。在仿真结果中,将通过与其他文献提出的可用带宽评估机制对比分析提出可用剩余带宽测量方法的准确性。     

A 802.11 Based Slotted Dual-Channel Reservation MAC Protocol for In-Building Multi-Hop Networks

In this paper, we propose a novel slotted Dual-Channel Reservation (DCR) MAC protocol that uses 802.11 primitives for providing both Quality of Service (QoS) and fairness. RTS/CTS handshaking is transmitted on a separated control channel to prevent successive collisions of RTS and CTS packets with existing data transmission. Furthermore, contention for channel access may be initiated by sender as well as receiver depending on the channel status for better fairness. A simple slot reservation algorithm in the data channel provides high efficiency. The main conclusion is that reservation access benefits both delay performance, and efficiency as well as fairness—the reason being that not only an exposed terminal can regain the channel more easily because of dramatically reduced contention (RTS-CTS) traffic, but also a hidden terminal receives less collisions in handshaking since any node winning a slot will quit contending on the control channel. Therefore, it is highly recommended to use reservation access even if the prevailing traffic is data, e.g. TCP. To enhance delay performance, we devise a fake packet repeating mechanism that can reserve the slot for a connection even if the user temporarily has no packets to transmit. Simulations based on key metrics—throughput, fairness index and mean delay are performed to validate the new protocol and quantify its advantages. The limitations of the proposed DCR-802.11 protocol due to need for global clock synchronization and dual channels are also discussed.Jing Zhu received the B.S. and M.Sc. degrees both in electronic engineering from Tsinghua University, Beijing, P. R. China, in 2000 and 2001, respectively, and Ph.D. in electrical engineering from University of Washington (Seattle) in 2004. Currently, he is a research scientist in the Communications Technology Lab at Intel Corp. He is an IEEE member. His main research interest is high-performance wireless networking and its applications, e.g. Internet-on-Move, Digital Home, and Intelligent Transport System, focusing on cross-layer protocol optimization.Sumit Roy received the B. Tech. degree from the Indian Institute of Technology (Kanpur) in 1983, and the M. S. and Ph. D. degrees from the University of California (Santa Barbara), all in Electrical Engineering in 1985 and 1988 respectively, as well as an M. A. in Statistics and Applied Probability in 1988. His previous academic appointments were at the Moore School of Electrical Engineering, University of Pennsylvania, and at the University of Texas, San Antonio. He is presently Prof. of Electrical Engineering, Univ. of Washington where his research interests center around analysis/design of physical and data link layer of communication systems, with a topical emphasis on next generation mobile/wireless networks. He is currently on academic leave at Intel Wireless Technology Lab working on high speed UWB radios and next generation Wireless LANs. His activities for the IEEE Communications Society includes membership of several technical committees and technical program committees for conferences, and he serves as an Editor for the IEEE Transactions on Wireless Communications and Wiley Journal on Wireless Communications and Mobile Computing.     

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.     

QoS provisioning for large-scale multi-ap WLANs

Large-scale deployment of IEEE 802.11 wireless LANs (WLANs) with a high density of access points (APs) has become commonplace due mainly to its potential for numerous benefits, such as ubiquitous service coverage, seamless handover, and improved link quality. However, the increased AP density can induce significant channel contention among neighboring cells, thus causing severe performance degradation and throughput imbalance between cells. There have been a plethora of research efforts to improve the WLAN performance, but most of them focused only on single WLAN environments without accounting for inter-cell contention. The de facto QoS-provisioning mechanism for WLANs, i.e., the Enhanced Distributed Channel Access (EDCA), is no exception to this. The EDCA focuses only on inter-flow priority distinction and has not considered the effect of inter-cell contention which significantly restricts its efficiency. This paper presents an enhanced QoS provisioning framework that takes into account inter-cell level differentiation as well as inter-flow level priority, which may be viewed as extension of QoS provisioning from a single-WLAN domain to a multi-WLAN domain. We also propose an architecture for managing multi-AP systems in which a central controller regulates the wireless channel occupancy of APs by adaptively configuring the cell-level QoS parameters. Our extensive simulation results show that the proposed inter-AP cooperative QoS scheme overcomes the limit of legacy 802.11e and provides a high level of fairness in large-scale densely-deployed WLANs.     

一种基于IEEE802.11支持QoS自适应调度器模型和算法

这篇文章提出了能够有效支持QoS的IEEE802．11自适应调度器模型。和以往的支持QoS的调度器模型相比，这里根据在主控接入点(MAP：Master Access Point)和用户终端(UT：User Termination)的各自延时需求对满足不同的传输机制的分组流进行自适应调度。这种机制不仅完全兼容当前支持QoS的IEEE802．11MAC协议标准，而且能够有效减少由于实时传输带来的分组延时，增加满足不同信道负载和带宽要求的数据流的吞吐率。实时测试得到的数据基本验证了这个要求。     

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.     

基于IEEE 802.11a的OFDM系统信道估计算法研究及实现

无线信道的复杂性和随机性使得信道估计在无线通信系统中的作用尤为重要.针对IEEE 802.11a协议以及无线衰落信道的特点,在MATLAB环境下建立系统仿真模型,采用相应的信道估计算法进行仿真.通过对算法性能以及复杂度的比较选择合适算法并在此基础上对算法进行改进.将改进后的算法在FPGA硬件平台上实现.仿真结果表明,该算法是一种较为理想的信道估计实现方案,具有较好的实用价值.     

Adaptive QoS Management for IEEE 802.11 Future Wireless ISPs

Wireless Internet Service Providers (WISPs) are expected to be the new generation of access providers using the emerging IEEE 802.11 technology. Face to the high competition of providing network services, the WISP have to offer the best service to the users. For this purpose, the WISP networks' managers need to provide Quality of Service (QoS) with a minimum cost in their wireless networks. The current link layer IEEE 802.11b provides fair sharing of the radio resource with no service differentiation mechanism; similarly to the Internet best effort service. However, the ongoing standard IEEE 802.11e should implement a priority mechanism at the link layer to differentiate the users' traffic. In order to overcome the lack of differentiated mechanism in the current link layer IEEE 802.11b, hence controlling the utilization of the scarce radio resource, we propose in this article to deploy Diffserv architecture coupled with an adaptive provisioning of QoS to provide better services to the users with minimum WISP cost and improve the utilization of the radio resource. Compliant with the current and future IEEE 802.11 link layer, the proposed adaptive QoS provisioning mechanism reacts to the radio resource fluctuation and improves the number of accepted clients in the IEEE 802.11 wireless cells based on the WISP business policies. The network layer differentiation provided by the Diffserv architecture intends to control the concurrent access of the traffic to the scarce radio resources at the IP layer of the mobile hosts for the uplink traffic on one hand, and at the IP layer of the base stations for the downlink traffic on the other hand.     

基于无线Mesh网络的分布式协调功能的研究

随着无线mesh网络的迅速发展和实时多媒体业务的日益增长,要求无线网络不仅能提供简单的连通性,还需要提供非常有效的QoS保证机制,针对这一问题,以时分多址/时分双工(TDMA/TDD)技术为基础,提出一种基于无线mesh网络的分布式协调功能,信道存取与数据传输发生在不同的时隙中,能够为端到端数据流公平的分配带宽,并且保证了实时服务传输的QoS.仿真及分析表明该协调功能可提高系统吞吐量并降低端到端延迟,有着更好的QoS性能.     

基于IEEE802．11b无线局域网支持QoS的盲检测算法

这里提出了一种基于IEEE802.11b无线局域网(WLANs)的MAC层的终端盲检测算法.和以往的算法相比,该算法通过对连接接入点AP(Access Point)的所有活动终端进行盲检测,可以非常有效的增加每个AP点所支持的语音通信终端数量,从而增加了信道的带宽,提高语音服务质量QoS.而且算法只执行在接入点的点协调功能上(PCF),因此不需要对当前的IEEE802.11MAC层的协议做任何修改.仿真结果表明了本算法对WLANs语音服务质量的有效支持.     

无线局域网在电力系统中的应用方案设计

简单介绍了无线局域网技术及其发展情况，给出了电力系统中的典型应用方案。以无线局域网技术为依托，结合最新的网络技术、VOIP语音技术及接口转换技术，可以提供一套全新的变电站、供电所通信通道整体解决方案，满足电力系统的话音、数据、图像及计算机联网的需求。     

IEEE802.11无线局域网视频流传输综述

With relatively high transmission capacity and usually unconstrained connections, IEEE802.11 WLANs provide the ideal infrastructure for pervasive video content sharing and communications. However, the delivery of high-performance video streams over 802.11 WLANs remains a challenging task due to the inherent characteristics of compressed video and dynamic channels. In this paper, we present a brief survey of various recent innovations that have been developed to enhance the Quality of Service (QoS) performance for video over WLANs. Based on the application scenarios, the solutions have focused mainly on three network layers, that is, Application layer (APP), Media Access Control layer (MAC), and Physical layer (PHY). After reviewing the video compression technology, we first examine various single-layer solutions for video over WLANs. We then discuss several cross-layer solutions that take advantage of mutual interactions between different network layers. Finally, several technical issues beyond QoS performance, including energy and security, are also addressed. We conclude that the application of video over WLANs will continue to increase in future.