802.11b DCF协议和802.11e EDCA协议性能仿真与分析

使用NS-2(Network Simulator Version 2)仿真软件,选取平均峰值信噪比、封包平均时延和封包最大时延3个指标对802.11b DCF和802.11e EDCA协议的流媒体通信性能进行仿真,通过改变最大封包长度分析比较该参数对2个协议性能的影响,研究结果表明了802.11e EDCA协议在多媒体通信业务中的优越性。     

Adaptive Power Saving Mechanisms for DCF in IEEE 802.11

Distributed Coordination Function (DCF) is the basis of IEEE 802.11 MAC sublayer. To improve energy efficiency, IEEE 802.11 has specified power saving mechanism (PSM) for DCF. However, the performance of PSM degrades seriously when load is heavy. In this paper we first analyze the reason of performance degradation, and then propose two adaptive mechanisms: PSM+ and fairPSM+. Numerous simulation results have shown that these two mechanisms can achieve high performance with heavy load and still get the same performance as PSM when load is light.Shihong Zou was born in 1978. He received his Bacchelor of Engineering degree in Computer Engineering from Nanjing University of Posts and Telecommunications (Nanjing, China) in 1999, and his Ph.D. degree in communication and information systems from Beijng University of Posts and Telecommunications (BUPT) in 2004. He is currently a lecturer in BUPT. His research interests include IP QoS, WLAN, mobile ad hoc networks and network security.Haitao Wu was born in 1976. He received his Bachelor of Engineering (B.E.) degree in Communication Engineering from Beijing University of Posts and Telecommunications (BUPT) in 1998, and his Ph.D. degree in communication and information systems from BUPT in 2003. He is currently a Post-doctor in Microsoft Research Asia (MSRA), wireless and networking group. His research interests include IP QoS, TCP/IP, wireless networks and peer-to-peer networks.Shiduan Cheng graduated in communication engineering at the Beijing University of Posts and Telecommunications (BUPT) in 1963. Since then she has been working at BUPT. From 1984 to 1987 and in 1994 she twice joined Alcatel Bell, Belgium as a visiting scholar, where she was involved in R&D work on ISDN and B-ISDN networks and systems. She became vice dean of the computer department of BUPT in 1987. From 1992 to 1999 she was the director of The National Key Laboratory of Switching Technology and Telecommunication Networks of BUPT. In the same duration she was also the head of The Switching and Networking Expert Group in 863 program, a national high-tech R&D plan organized by The Ministry of Science and Technology of China. She has published more than 100 papers and several books in the field of telecommunications. She is currently the vise director of Standing Committee of Science of BUPT. Her research interests cover ISDN, ATM, TCP/IP, switching software, protocol engineering, traffic engineering, network performance, QoS, security and survivability. Currently she is working on QoS control, measurement and management for the next generation Internet.     

路由特性对IEEE802．11 DCF多跳网络容量的影响

使用数学分析方法研究基于IEEE 802.11 DCF的Ad Hoc网络中节点传输半径和路由策略选择问题.在节点均匀分布的多跳网络中,使用四种路由策略以及不同的节点传榆半径设王,试图找出能够使网络容量最大化的方案组合.计算结果表明,在节点密度一定的情况下,减小网络节点的传输距离有利于增加网络的容量,而在传输半径一定的条件下,使用能够导致长跳路由的策略,有利于提高网络容量.     

A Novel Event Model for Performance Analysis of IEEE 802.11 DCF

After considering the memory effect among series events occurring on the channel, we propose a novel event model to analyze the channel status more precisely. The memory effect is caused by the backoff freezing regulation of IEEE 802.11 Distributed coordination function （DCF）, which has been ignored before and thus resulted in the inaccurate evaluation of the network performance. Based on our new event model, the network performance of IEEE 802.11 DCF, including throughput, packet delay distribution and energy efficiency is analyzed. Simulation results show that our model is highly accurate.     

The Impact of RTS Threshold on Capacity of IEEE 802.11 DCF

Distributed coordination function (DCF) is the fundamental medium access control (MAC) mechanism in IEEE 802.11[1]. There are essentially two MAC techniques in DCF: a basic access method that uses two-way handshaking (DATA-ACK) and a RTS/CTS variant that uses Request-To-Send and Clear-To-Send messages in a four-way handshake (RTS-CTS-DATA-ACK). In a hybrid system, there is a preconfigured RTS threshold. Packet with payload longer than this threshold is transmitted in RTS/…     

IEEE802．11DCF／PCF机制仿真与分析

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。     

Modeling Channel Access Delay and Jitter of IEEE 802.11 DCF

With the ever-increasing requirement of WLAN to support real-time services, it is becoming important to study the delay properties of WLAN protocols. This paper constructs a new model to analyze the channel access delay and delay jitter of IEEE 802.11 DCF in saturation traffic condition. Based on this analytical model, average channel access delay and delay jitter are derived for both basic access and RTS/CTS-based access scheme. The accuracy of the analytical model is validated by simulations and furthermore we discuss the impact of initial contention window, maximal backoff stage, and packet size on channel access delay and delay jitter of 802.11 DCF using the proposed model.

有限负载下802.11 DCF的性能分析及优化

利用三维马尔可夫链和M/G/1/K队列建立了有限负载下DCF机制的性能模型,分析了终端数量、传输负载、二进制指数回退机制及MAC层有限队列对系统性能的影响.基于该模型,推导了有限负载下最大化吞吐量的最优最小竞争窗口的闭式解.仿真结果表明,模型能够有效地预测有限负载下DCF的性能,根据传输负载调整最小竞争窗口大小能够获得最大化吞吐量.     

On the Capacity of IEEE 802.11 DCF with Capture in Multipath-Faded Channels

In this paper, we estimated the influence of capture effect over the capacity of IEEE 802.11b DCF within a single picocell. The channel utilization is examined analytically by introducing two capture models based on Rayleigh-distributed envelopes of the captured and the interfering frames divided into two local-mean power classes. Simulations in a pure Rician-faded channel depict the conditions under which both Rayleigh-faded capture models can be used to accurately predict the peak network capacity. Unlike the RTS/CTS handshake access mode, Basic access mode is significantly sensitive to the capture ratio, i.e., the receiver design. The packet size threshold over which it is convenient to switch from Basic to RTS/CTS handshake access scheme is also sensitive to the capture effect.     

A Novel Random Backoff Algorithm to Enhance the Performance of IEEE 802.11 DCF

The Probability Distribution of Slot Selection (PDoSS) of IEEE 802.11 DCF is extremely uneven, which makes the packet collision probability very high. In this paper, we propose a novel RWBO+BEB backoff algorithm for 802.11 DCF to make the PDoSS even and thus decrease the packet collision probability. A Markov model is built for analyzing RWBO+BEB's PDoSS and saturation throughput. The model's correctness is validated by simulation. The performance of RWBO+BEB is also evaluated by simulation in terms of PDoSS, saturation throughput, packet collision probability and packet delay. The simulation results indicate that RWBO+BEB can decrease the packet collision probability to a large extent, utilize the channel more efficiently, and make the packet delay jitter much lower comparing to 802.11 DCF. Moreover, we analyze the relation of saturation throughput and packet collision probability to walking probability (p_d) and contention windows (w), respectively. The analysis indicates that RWBO+BEB has a remarkable feature: its saturation throughput keeps high, and packet collision probability keeps very low (which under 0.1) in a large range of p_d and w, this allows us to configure p_d and w more flexibly. Supported by the Program for New Century Excellent Talents in University (NCET 2005), the Research Project of Chongqing Municipal Education Commission of China (KJ050503), the Research Grants by the Science & Tech. Commission of Chongqing (8817) and the National Science Foundation of China (90304004). Li Yun was born in 1974. He is currently a Ph.D. candidate in University of Electronic Science and Technology of China. His research interests are in MAC protocol improvement and QoS in wireless ad hoc networks. Long Ke-Ping was born in 1968. He received his Ph.D. from University of Electronic Science and Technology of China in 1999. He is a professor Ph.D. supervisor in special research Centre for Optical Internet and Wireless Information Networks (COIWIN) at ChongQing University of Posts and Telecommunications. He was an IEEE member. He has over 120 research publications and 4 patents application. His research interests include: Optical Burst switching, modeling of optical networking, IP QoS mechanisms (Diffserv and Intserv, MPLS), WDM/SDH/ATM networks survivability, TCP/IP enhancements in wireless networks, and Mobile IP. Zhao Wei-liang was born in 1962 and received his Ph.D. degree from University of Electronic Science and Technology of China in 2001. He is a professor and a post-doctoral fellow in Beijing University of Posts & Telecommunications of China. His current interest lies in wireless communications.     

The Analysis of System Capacity of VoIP System Supporting CBRand VBR Traffic in IEEE802.11b WLAN Under DCF Mode

1IntroductionVoIP over IEEE802 .11[1]WLANis supposedto be-come an i mportant application. The IEEE 802 .11 hastwo different channel accessing mechanisms , namely,the DCFand Point Coordination Function (PCF) .DCFis based onthe Carrier Sense Multiple Access with Colli-sion Avoidance (CSMA/CA) channel accessing mecha-nism, while PCF is based on the polling technique .Here we only consider that the wireless networks oper-ate using the DCF MAC protocol ( without theRTS/CTS mech…     

无线网络能效的优化与评估

文章从能效测度入手,对已有的无线网络能效测度评价体系进行了讨论,并提出以碳排放量为标准和与网络负载相结合的能效测度模型。在能效测度模型的基础上,文章提出减少设备使用、无线资源调度、节点协作等一系列无线网络能效优化方法,并建议在无线网络协议架构中加入能效监控和能效评估模块。文章还对无线网络能效优化和评估方法中存在的技术挑战进行了展望。     

IEEE 802.11 DCF对TCP性能的影响及算法改进

本文讨论了IEEE 802.11 DCF两种方式(RTS/CTS和CSMA/CA)混合工作时TCP的性能,发现高负载时TCP流存在不稳定的问题.基于此提出了RWB(Reserve Window Backoff)算法,该算法从联合优化的角度出发,减轻了WLAN MAC接入机制和TCP拥塞控制之间的不良影响,从而提高了TCP的吞吐量,改善了TCP流的稳定性.文中通过仿真对算法进行了分析和研究.     

IEEE 802.11在无线自组网中的应用研究

深入分析了IEEE 802.11 DCF机制应用于无线自组网存在的固有缺陷及潜在原因,并阐明了数据流竞争、物理层机制对MAC协议性能的影响。IEEE 802.11 DCF是针对全连通adhoc网络结构设计的,分析表明,要在实际的多跳无线自组网中应用还存在很多问题需要解决。在此基础上提出了将IEEE 802.11有效应用于多跳无线自组网的进一步研究方向。     

Comprehensive Analysis of the IEEE 802.11

Wireless Local Area Networks (WLANs) have attracted significant research interest over the past few years. The IEEE 802.11 standard is the most mature technology for WLANs and has been widely adopted for wireless networks. This paper outlines a new performance analysis for IEEE 802.11 Distributed Coordinated Function (DCF) using Direct Sequence Spread Spectrum (DSSS) in terms of the channel throughput, packet processing rate, packet loss probability and average packet delay using a perfect channel as well as a slow Rayleigh fading channel. The theoretical results are subsequently compared with the simulation results. It is shown that there is a good match between these two results, which validates the analytical model.Peter P. Pham received the B.E. in computer system engineering (honour) from the University of Adelaide, Australia in December 2000. After graduation, he worked as a software engineer for Motorola for 6 months in Singapore. Since August 2001, he received a President scholarship and started as a Ph.D. candidate at Institute for Telecommunications Research, the University of South Australia. His area of interests are performance analysis and coding techniques for ad hoc networks.     

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.     

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。     

5G智能增强型能效优化技术

全球化能源危机和环境问题使得能源效率成为无线通信设备的一个核心指标.能源效率最大化已上升到国家战略层面,成为全球范围内的研究热点.针对现有能效优化模型普遍存在的计算复杂度高和效率低的问题,提出智能增强型全局优化策略.基于信道状态信息对大规模MIMO系统进行收发两端的分布式重构处理,得到不同信道状态条件下高效的多维资源融...     

Comparative Study of 802.11 DCF and its Modification in the Presence of Noise

IEEE 802.11 specifies a technology for wireless local area networks (LANs) and mobile networking. In this paper, we present an analytical method of estimating the saturation throughput of a 802.11 wireless LAN in the presence of noise, which distorts transmitted frames. With the Distributed Coordination Function (DCF) being the fundamental access mechanism in the IEEE 802.11 MAC protocol, sequential attempts to transfer by every station are separated by backoff intervals. Besides the standard backoff rule of the DCF, according to which the mean backoff interval is doubled after each failure in order to avoid collisions, we propose and study a modification of the backoff rule. This modification relies on the optional 802.11 tools to recognize a reason of a failure (collision or noise-induced distortion) and does not increase the mean backoff interval if a failure happens due to distortion by noise. In addition to the throughput, our method allows estimating a probability of a packet rejection occurring when the number of packet transmission retries attains its limit. The obtained numerical results of investigating 802.11 LANs by the developed method are validated by simulation and show high estimation accuracy for any values of protocol parameters and bit error rates. We adopt this method to tune the protocol parameters and to compare the proposed modification with the standard backoff rule. This work was partially supported by NATO Science Programme in the Collaborative Linkage Grant PST.CLG.977405 “Wireless Access to Internet exploiting the IEEE 802.11 technology”. Andrey I. Lyakhov is a leading researcher of the Institute for Information Transmission Problems of Russian Academy of Sciences, Moscow, Russia. Since 1982, his research interests have been in performance evaluation of parallel and distributed computer and communication systems, including multiprocessors and local area cable networks, using both queuing theory methods and asymptotic analysis of large scale queuing networks. His recent interest is in estimating the performance indices of local and metropolitan area wireless networks. Dr. Lyakhov received a M.S. degree in computer science from Moscow Engineering and Physics Institute in 1983, and Candidate and Doctoral Degrees in computer science from the Institute of Control Sciences of Russian Academy of Sciences (Moscow, Russia) in 1989 and 1996, respectively. He has written a textbook in multiprocessor study and published more than 50 papers in refereed journals and conferences. Vladimir M. Vishnevsky is a full professor, and a deputy director and a head of department of the Institute for Information Transmission Problems of Russian Academy of Sciences, Moscow, Russia. Since 1971, his principal research interests have been in developing mathematical methods based on the queuing theory for performance analysis and structure optimization of computer and communication systems and networks. His current interests include topological design of large-scale communication networks and performance evaluation of wireless networks. Prof. Vishnevsky received a M.S. degree in computer science from Moscow Institute of Electronic and Mathematics in 1971, and Candidate and Doctoral Degrees in computer science from the Institute of Control Sciences of Russian Academy of Sciences (Moscow, Russia) in 1974 and 1989, respectively. He has written three textbooks in communication network study and design and published more than 100 papers in refereed journals and conferences. He is an associate member of the IEEE and an active member of the New York Academy of Sciences. In addition to serving as a program committee member of various conferences, Prof. Vishnevsky serves as a member of editorial boards of such journals as Automation and Remote Control and Electronica (in Russian).