自适应EDCF方法分析

简述了IEEE802.11e的访问控制机制中的增强型分布式协调功能(Enhanced Distributed Coordination Function,EDCF),针对IEEE802.11e QoS机制在高负载情况下业务性能下降的问题,提出了一种新的基于EDCF的自适应方法,并用OPNET软件进行了仿真实现。仿真结果表明,该方法能够有效减少网络传输的延时,显著提高数据吞吐量,极大地改善了QoS的性能。     

一种基于IEEE802.11EDCF的自适应能量调整算法

简述了IEEE802.11及IEEE802.11e的两种访问控制机制DCF和EDCF,提出了一种基于IEEE802.11 EDCF的自适应能量调整算法,并在NS2上进行了仿真实现.仿真实验结果表明,该算法能够根据分组的优先权水平和节点当前能量值动态调度信道接入,延长了全网的生存期.     

IEEE802.11 n信道编译码器的FPGA设计

首先分析了新一代无线局域网标准IEEE802.11n的卷积编译码原理,然后给出了卷积编码器和Viterbi译码器的FPGA实现方法,其中Viterbi译码器采用并行结构和回溯译码算法.最后进行了综合仿真,结果表明,设计的编译码器能够实现高速率编译码,满足IEEE802.11n高速吞吐量的要求.     

TCP在WLAN中的性能提高与分析

IEEE 802.11被用于支持无线以太网(WLAN)中的分组传输.分布式协调功能(DCF)是IEEE 802.11的MAC协议的基本方式.为提高传输控制协议(TCP)在WLAN上的性能,本文提出了DCF+,并引入了分析模型对DCF及DCF+在WLAN上的吞吐量性能进行分析.建模及仿真结果表明本文提出的DCF+可以提高TCP在WLAN上的性能.     

Ad hoc网络中DCF公平性分析与改进

在考虑节点的物理载波检测范围大于通信范围的情况下,该文分析了多跳Adhoc网络中物理载波检测机制对IEEE 802.11DCF协议公平性的影响。针对载波干扰给IEEE802.11DCF协议带来的严重不公平问题,提出了一种基于冲突和干扰感知的退避(CIAB)算法。仿真证明,该算法能有效地改善IEEE802.11DCF协议的公平性,并且没有引起网络吞吐量的严重下降。     

无线传感器网络功耗控制分析与仿真

根据无线通信原理为三种MAC协议(IEEE802.11MAC、BASIC、PCM)建立了能耗分析模型,对功率控制给网络带来影响进行了数学分析.并对三种MAC协议在不同网络规模中的吞吐量、能量效率进行仿真比较.仿真结果表明:有效的控制节点的发射功率,在减少能耗的同时,可以提高网络性能.     

一种车载网络的簇间碰撞避免MAC协议

车载网络采用IEEE802.11p作为底层协议来保证通信的可靠性,IEEE1609.4标准是IEEE802.11p的拓展。然而,这种基于IEEE1609.4标准的信道访问机制存在一些不足。本论文提出一种保证安全信息的可靠传输,提高服务信道的吞吐量的基于簇的碰撞避免的MAC协议。     

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IEEE 802.11a/g的视频传输系统

介绍了一种基于IEEE 802.11a/g无线传输DVD视频信号的系统.介绍了IEEE 802.11a/g协议的特点及其一些重要的技术机制,阐述了基于该协议实现视频传输的优势和应用前景,以DVD无线视频传输为例,介绍了基于IEEE 802.11a/g和嵌入式系统的无线视频传输的实现方案,概述了它的系统结构、工作流程和软件部分所要完成的工作,分析了实现过程中的若干关键技术.     

IEEE802.11MAC协议中一种改进的退避解决算法

IEEE802.11无线局域网,在共享信道中经历碰撞的网络节点需要随机退避一段时间,这段时间是从竞争窗口中均匀选取,竞争窗口大小由BEB机制动态控制,一些文献研究表明,BEB机制在重负载的情况下,突现出公平性问题和低的吞吐量,本文基于MILD退避机制,提出一种适用于分布式协调功能改进算法。该算法通过修改802.11的MAC层中的DCF(DistributedCoordinationFunction)子协议,改善了IEEE802.11无线局域网在拥塞情况下的性能,提高了网络吞吐量。     

IEEE 802．11网络分析模型

IEEE 802.11在MAC层采用DCF作为主要的信道接入方式。本文分析了现有的几种802.11网络分析模型,其中B ianch i模型很好的描述了饱和状态下802.11 DCF的性能;X iao模型针对802.11e进行了多优先级的扩展,实现了EDCF的性能分析。最后介绍了一种新的分析模型,新模型同时考虑了业务优先级和内部调度算法,够较准确地描述网络性能。     

A dynamic location management service for group applications in cellular networks

To cope with the increasing demand of multimedia applications, new IEEE 802.11 wireless local area networks devices have been defined such as IEEE 802.11aa and IEEE 802.11ac. The former proposes new intra-access categories (AC) differentiation based on stream classification service (SCS) scheme. The latter standard allows simultaneous downlink transmissions thanks to downlink multi-user MIMO technology and sharing transmission opportunity (TXOP) period scheme. In this paper, we focus on the basis of this technique and the behavior of the access point (AP) to manage the multi-user access. Then, we propose a hybrid access mechanism entitled multi-user multi-cast access mechanism (MUMAM) that supports downlink multi-user transmissions while considering intra-AC differentiation. MUMAN considers SCS scheme to prioritize between multicast and unicast flows of an AC and follows transmissions based on IEEE 802.11ac TXOP sharing technique. Extensive simulation and analysis show that MUMAM has a significant positive impact on delay and throughput performance of different AC(s).     

基于接入控制机制的无线局域网MAC协议

本文对IEEE 802.11无线局域网点协调功能的改进协议(MPCF)的性能进行深入的研究.MPCF基于接入控制和链式轮询机制.根据业务特点,MPCF协议分别为实时业务和非实时业务提供不同的服务策略:实时业务采用ACK应答方式,非实时业务采用无ACK应答方式,从而引入接入控制机制,更好地保证实时业务的服务质量.为了提高网络吞吐量,MPCF协议采用链式轮询机制.本文给出MPCF吞吐量的分析模型.仿真结果表明:MPCF协议的性能优于PCF协议,而且理论分析结果与仿真结果基本吻合.     

Quality of service support in IEEE 802.11 wireless ad hoc networks

Supporting Quality of Service (QoS) in wireless networks is a challenging problem. The IEEE 802.11 LAN standard was developed primarily for elastic data applications. In order to support the transmission of real-time data, a polling-based scheme called the point coordination function (PCF) was introduced in IEEE 802.11. However, PCF was not able to meet the desired and practical service differentiation requirements to fulfill the need of real-time data. Therefore, Task Group E of the IEEE 802.11 working group released several IEEE 802.11e drafts, whose main task is to support QoS in IEEE 802.11 LANs. The polling scheme of PCF is extended in IEEE 802.11e into the more complex hybrid coordination function (HCF). We found that HCF has several performance issues that may affect its anticipated performance. In this paper, we address these issues and propose a QoS enhancement over PCF, called enhanced PCF (EPCF) that enables Wireless LAN to send a combination of voice, data and isochronous data packets using the current IEEE 802.11 PCF. First, we compare the performance of the proposed model (EPCF) with the HCF function of the IEEE 802.11e through simulation. Second, we extend the proposed model (EPCF) to work in a multihop wireless ad hoc mode and present the advantages and limitations in this case. Simulation results demonstrate an enhanced performance of our scheme over the legacy PCF and a comparable performance to the IEEE 802.11e HCF in terms of the average delay and system throughput. However, EPCF is much simpler than HCF, provides flow differentiation, and is easy to implement in the current IEEE 802.11 standard.     

Throughput and QoS optimization for EDCA-based IEEE 802.11 WLANs

The enhanced distributed channel access (EDCA) mechanism has been adopted by both the IEEE 802.11e standard and the Multiband OFDM Alliance (MBOA) for quality of service (QoS) provisioning in high speed wireless LANs and UWB-based wireless PANs. Based on an analytical model of EDCA, this paper presents an optimal solution to providing maximum system throughput while maintaining the service differentiation among traffic classes. Contention window sizes are adapted to achieve throughput optimization according to the throughput ratio and number of active stations of each traffic class. To overcome the difficulty of accurate estimation of the number of competing stations we propose to use the method of subrange partitioning. An admission control scheme is also discussed. Simulation results demonstrate the effectiveness of the proposed MAC optimization framework.     

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.     

A fragment‐based retransmission scheme with quality‐of‐service considerations for wireless networks

In order to satisfy quality‐of‐service requirements for real‐time multimedia applications over wireless networks, IEEE 802.11e has been proposed to enhance wireless‐access functionalities. In IEEE 802.11e, collisions occur frequently as the system load becomes heavy, and then, the latency for successfully transmitting data is lengthened seriously because of contention, handshaking, and backoff overheads for collision avoidance. In this paper, we propose a fragment‐based retransmission (FBR) scheme with quality‐of‐service considerations for IEEE 802.11e‐based wireless local area networks. Our FBR can be used in all proposed fragmentation‐based schemes and greatly decrease redundant transmission overheads. By utilizing FBR, the retransmission delay will be significantly improved to conform strict time requirements for real‐time multimedia applications. We develop an analytical model and a simulation model to investigate the performance of FBR. The capability of the proposed scheme is evaluated by a series of simulations, for which we have encouraging results. Copyright © 2011 John Wiley & Sons, Ltd.     

Statistical characterization of the service time in saturated IEEE 802.11 networks

In this paper, we propose an analytical model for the service time in saturated IEEE 802.11 DCF networks. We derive a closed-form probability generating function for the packet service time of a cluster of IEEE 802.11 terminals, both for the RTC/CTS and the basic access mode. The probability generating function is inverted by numerical methods, providing the probability distribution function of the service time. Interestingly, it catches certain features of the DCF service time, which cannot be revealed with the second order analysis known in the literature. Finally, this analytical model is validated by means of extensive simulation outcomes.     

A traffic control system for IEEE 802.11 networks based on available bandwidth estimation

To support Quality of service (QoS)‐sensitive applications like real‐time video streaming in IEEE 802.11 networks, a MAC layer extension for QoS, IEEE 802.11e, has been recently ratified as a standard. This MAC layer solution, however, addresses only the issue of prioritized access to the wireless medium and leaves such issues as QoS guarantee and admission control to the traffic control systems at the higher layers. This paper presents an IP‐layer traffic control system for IEEE 802.11 networks based on available bandwidth estimation. We build an analytical model for estimating the available bandwidth by extending an existing throughput computation model, and implement a traffic control system that provides QoS guarantees and admission control by utilizing the estimated available bandwidth information. We have conducted extensive performance evaluation of the proposed scheme via both simulations and measurements in the real test‐bed. The experiment results show that our estimation model and traffic control system work accurately and effectively in various network load conditions without IEEE 802.11e. The presence of IEEE 802.11e will allow even more efficient QoS provision, as the proposed scheme and the MAC layer QoS support will complement each other. Copyright © 2006 John Wiley & Sons, Ltd.     

A Load-Balancing and Push-Out Scheme for Supporting QoS in MANETs

Currently, mobile ad hoc networks (MANETs) lack load-balancing capabilities, and thus, they fail to provide good performance especially in the case of a large volume of traffic. Ad hoc networks lack also service differentiation. However, in these wireless environments, where channel conditions are variable and bandwidth is scarce, the differentiated services developed for the Internet are suboptimal without lower layers' support. The IEEE 802.11 standard for Wireless LANs is the most widely used WLAN standard today. It has a mode of operation that can be used to provide service differentiation, but it has been shown to perform badly. In this paper, we present a simple but very effective method for support Quality of Service, by the use of load-balancing and push-out scheme. This approach offers to the mobile node: the ability to alleviate congestion by traffic distribution of excessive load, and to support priority of packets in the single MAC buffer. We evaluate the performance of our algorithm and compare it with the original IEEE 802.11b protocol. Simulation results show that this new approach reduces packet loss rate and increases throughput as well as provides service differentiation in the MAC layer.