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无线局域网QoS机制解析 总被引:1,自引:0,他引:1
无线局域网(WLAN)技术的发展带来的多媒体业务流量的剧增,使无线网络的资源管理、服务质量(QoS)保障等问题日益突出,传统的媒体访问控制(MAC)协议需要重新设计才能有效地解决无线网络的QoS问题。本文介绍了无限局域网QoS技术的发展,包括针对IEEE802.11 MAC层协议进行的各种QoS增强技术。通过与传统的802.11标准的MAC层进行对比分析.讨论了IEEE802.11e的2个新策略: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。 相似文献
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无线局域网(WLAN)技术的发展带来的多媒体业务流量的剧增,是无线网络的资源管理、服务质量(QoS)保障等问题日益突出,传统的媒体访问控制(MAC)协议需要重新设计才能对无线网络的QoS问题进行有效的解决。本文介绍了无限局域网QoS技术的发展,包括针对IEEE802.11MAC层协议进行的各种QoS增强技术。通过与传统的802.11标准的MAC层进行对比分析,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。 相似文献
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传统的IEEE802.11无线局域网环境下承栽VolP(Voice over IP)语音业务时,QoS和接入容量都严重受损,成为制约VoWLAN发展的瓶颈。文章以XG729编码的语音包在IEEE802.11b长PPDU模式传输的帧为例,通过分析VoIP包成帧效率、IEEE802.11b成帧效率和DCF协议效率,得到饱和条件下归一化系统吞吐率;同时计算出IEEE802.11a/b协议下VoIP语音理论传输容量,为进一步提升IEEE802.11无线局域网环境下语音传输能力研究提供基础。 相似文献
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随着无线网络的迅速发展,网络上的业务流量与日俱增,如何保证无线局城网实时业务服务质量的问题也越来越突出.文中分别介绍了IEEE802.11中的MAC层协议和802.11e标准中所采纳的改进方式,通过对比分析DCF和EDCF的性能特性,具体仿真时延和丢包率两个性能参数,指出了802.11e标准对MAC层所做的改进. 相似文献
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首先对IEEE802.11的关键技术进行了简要的阐述,包括载波监听碰撞避免机制、隐藏节点和暴露节点问题、RTS/CTS握手机制以及MAC的分布式协调功能和点协调功能。实现了PCF机制的代码并用NS-2对DCF和PCF机制进行了仿真,验证了协议的实现,从时延和吞吐量方面对两个机制的性能进行比较和分析。 相似文献
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IEEE802.11系列标准是无线局域WLAN(Wireless Local Area Network)中应用最广的标准。其中IEEE802.11a工作在5.8GHz频段,除了不受向下兼容性的限制外,同频段系统之间的干扰也很小,因而比较适合高密度、高容量的网络。IEEE802.11a采用正交频分复用(OFDM)调制方式,理论最高传输速率可达54Mbit/s,但在实际应用中,其传输净数据率均远低于此。为了评估其数据业务支持能力,指导网络容量规划,文章主要从MAC层协议性能方面对IEEE802.11a WLAN网络的性能进行了分析,并给出了其实际吞吐量。 相似文献
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将于2009年年底推出正式技术规范的IEEE802.11n已成为目前业界的焦点之一。802.11n基于之前的IEEE802.11标准,增加了MIMO(多入多出)技术、在PHY层的信道绑定,以及MAC层的帧聚合,是IEEE802.11-2007无线网络技术的重要补充。原始数据速率达到了54 Mbps,最高可达600 Mbps。 相似文献
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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. 相似文献
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A scheduling algorithm for QoS support in IEEE802.11 networks 总被引:2,自引:0,他引:2
This article presents a scheduling algorithm for the IEEE 802.11e hybrid coordination function under definition by the IEEE 802.11e task group. HCF can be used to provide IP quality of service guarantees in IEEE802.11e infrastructure WLANs. The enhanced distributed coordination function is mainly used for data transmission without QoS guarantees, but can also be used to decrease the transmission delay of QoS-sensitive traffic. Scheduling of queued packets follows a delay-earliest-due-date algorithm. The proposed algorithm is compatible with the link adaptation mechanisms implemented in commercial WLANs, as it limits the amount of time during which the stations control the wireless medium. The performance of the algorithm is evaluated through computer simulation and compared with the reference scheduler presented by the IEEE 802.11e task group. 相似文献
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Mir Hamza Mahmood Cheng-Chun Chang Daewon Jung Zhi-Hong Mao Hyuk Lim Heung-No Lee 《AEUE-International Journal of Electronics and Communications》2010,64(11):1031-1041
Conventional IEEE 802.11 medium access control (MAC) protocol discourages simultaneous transmission to avoid collisions. With fast advances in physical layer technologies, multi-user detection (MUD) capable receivers which can detect multiple frames from different users simultaneously become available. If we are to utilize them in today's wireless LAN, however, it is not entirely clear how we should change the MAC and how much benefit is available and can be obtained by doing so. The primary objective of this paper is to investigate such questions. We approach this objective by developing a new throughput expression for 802.11 distributed coordination function (DCF). The derived expression has been verified in simulation. We show that significant throughput gain can be garnered with slight modification in 802.11 DCF. 相似文献
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IEEE 802.11 Wireless Local Area Networks 总被引:20,自引:0,他引:20
The draft IEEE 802.11 wireless local area network (WLAN) specification is approaching completion. In this article, the IEEE 802.11 protocol is explained, with particular emphasis on the medium access control sublayer. Performance results are provided for packetized data and a combination of packetized data and voice over the WLAN. Our performance investigation reveals that an IEEE 802.11 network may be able to carry traffic with time-bounded requirements using the point coordination function. However, our findings suggest that packetized voice traffic must be handled in conjunction with an echo canceler 相似文献
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This paper addresses the issue of real-time data transmission in vehicles to roadside (V2R) environment by the hybrid coordination function (HCF) of controlled channel access (HCCA) specified by the IEEE 802.1 lp standard. HCCA is one of the medium access mechanisms in the IEEE 802.11 standard, and uses the polling scheme similar to the point coordination function (PCF) to provide reliable quality of service (QoS), which may cause resource overshooting and high time consuming. This paper tries to improve the performance of the HCCA polling scheme and designs new data transmission scheduling scheme. The simulation results of the proposal are compared with those of the standard strategy. Simulation results demonstrate that the improved HCCA has lower delay, loss rate, and higher throughput than those of the standard one. 相似文献
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Lixiang Xiong Guoqiang Mao 《Communications Letters, IEEE》2007,11(9):759-761
In this letter, we propose a novel Markov chain model for IEEE 802.11 WLAN, considering a commonly used data rate switching mechanism. In the proposed model, both collision and transmission errors are considered. The performance of IEEE 802.11 DCF (distributed coordination function) is analyzed using the proposed model. The accuracy of the proposed model is verified by simulation. 相似文献
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Jaehyuk Choi Joon Yoo Chong-kwon Kim 《Communications Letters, IEEE》2006,10(5):335-337
This letter presents a novel analytic model that accurately evaluates the performance of a single-hop IEEE 802.11 wireless LAN (WLAN). By using a closed queuing network, we model an IEEE 802.11 WLAN system that consists of a fixed number of stations and derive the saturated throughput of the IEEE 802.11 distributed coordination function (DCF). The ns-2 simulation results show that our new analysis model is very accurate in evaluating the performance of the IEEE 802.11 DCF. 相似文献
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Xiaoying Zhang Lei Guo Alagan Anpalagan Ahmed Shaharyar Khwaja 《Wireless Personal Communications》2017,92(3):843-861
This paper presents an energy-efficient cooperative MAC (EECO-MAC) protocol using power control in mobile ad hoc networks. Cooperative communications improve network performance by taking full advantage of the broadcast nature of wireless channels. The power control technique improves the network lifetime by adjusting the transmission power dynamically. We propose the best partnership selection algorithm, which takes energy consumption into consideration for selection of the optimal cooperative helper to join in the transmission. Through exchanging control packets, the optimal transmission power is allocated for senders to transmit data packets to receivers. In order to enhance energy saving, space–time backoff and time–space backoff algorithms are proposed. Simulation results show that EECO-MAC consumes less energy and prolongs the network lifetime compared to IEEE 802.11 DCF and CoopMAC at the cost of delay. Performance improvement offered by our proposed protocol is apparent in congested networks where nodes have low and limited energy. 相似文献
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Quality-of-service provisioning system for multimedia transmission in IEEE 802.11 wireless LANs 总被引:2,自引:0,他引:2
Der-Jiunn Deng Hsu-Chun Yen 《Selected Areas in Communications, IEEE Journal on》2005,23(6):1240-1252
IEEE 802.11, the standard of wireless local area networks (WLANs), allows the coexistence of asynchronous and time-bounded traffic using the distributed coordination function (DCF) and point coordination function (PCF) modes of operations, respectively. In spite of its increasing popularity in real-world applications, the protocol suffers from the lack of any priority and access control policy to cope with various types of multimedia traffic, as well as user mobility. To expand support for applications with quality-of-service (QoS) requirements, the 802.11E task group was formed to enhance the original IEEE 802.11 medium access control (MAC) protocol. However, the problem of choosing the right set of MAC parameters and QoS mechanism to provide predictable QoS in IEEE 802.11 networks remains unsolved. In this paper, we propose a polling with nonpreemptive priority-based access control scheme for the IEEE 802.11 protocol. Under such a scheme, modifying the DCF access method in the contention period supports multiple levels of priorities such that user handoff calls can be supported in wireless LANs. The proposed transmit-permission policy and adaptive bandwidth allocation scheme derive sufficient conditions such that all the time-bounded traffic sources satisfy their time constraints to provide various QoS guarantees in the contention free period, while maintaining efficient bandwidth utilization at the same time. In addition, our proposed scheme is provably optimal for voice traffic in that it gives minimum average waiting time for voice packets. In addition to theoretical analysis, simulations are conducted to evaluate the performance of the proposed scheme. As it turns out, our design indeed provides a good performance in the IEEE 802.11 WLAN's environment, and can be easily incorporated into the hybrid coordination function (HCF) access scheme in the IEEE 802.11e standard. 相似文献