基于效用最大化的IEEE 802.11 DCF性能分析及改进

针对802.11 DCF在系统负载较大时不能有效利用带宽资源的缺点,该文提出一种基于效用函数的DCF优化机制(U-DCF)。通过设置站点吞吐量的对数效用函数,将带宽资源的有效利用问题建模为系统效用最大化问题;应用最优化理论将此系统问题等效为可分布式求解的用户问题,即各站点只须独立选择最大化其净效用的竞争参数(CWmin),则系统整体效用也获得最大化。仿真结果表明：与标准DCF相比,U-DCF通过预估系统的当前平均分组长度和竞争站点数来调整竞争参数CWmin,能够显著提高系统的饱和吞吐量,减小分组发送时延和丢帧率。     

Performance analysis of IEEE 802.11 DCF with stochastic reward nets

In this paper, we present a performance study to evaluate the mean delay and the average system throughput of IEEE 802.11‐based wireless local area networks (WLANs). We consider the distributed co‐ordination function (DCF) mode of medium access control (MAC). Stochastic reward nets (SRNs) are used as a modelling formalism as it readily captures the synchronization between events in the DCF mode of access. We present a SRN‐based analytical model to evaluate the mean delay and the average system throughput of the IEEE 802.11 DCF by considering an on–off traffic model and taking into account the freezing of the back‐off counter due to channel capture by other stations. We also compute the mean delay suffered by a packet in the system using the SRN formulation and by modelling each station as an M/G/1 queue. We validate our analytical model by comparison with simulations. Copyright © 2006 John Wiley & Sons, Ltd.     

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.     

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.

IEEE802.11 DCF发送过程的能耗分析

该文通过数学模型分析网络处于饱和状态时,终端采用DCF的基本方式和RTS/CTS方式发送一个固定长度的数据包所需要消耗的能量。进而,得到数据包载荷长度在给定的区间上服从一定的分布条件下,RTS门限和终端发送一个数据包所需消耗能量的平均值之间的关系。研究发现,存在一个使终端发送的平均能耗最小的最佳RTS门限,给出了最佳RTS门限的求解方法。计算机仿真结果很好地验证了理论分析的正确性。     

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.     

IEEE 802.11b DCF三维Markov非饱和链路模型

为了准确评估实际网络中IEEE 802.11b分布式协调功能(Distributed Coordination Function,DCF)的系统性能,提出了一种三维Markov链路模型,该模型综合考虑了DCF协议退避计数器冻结状态和有限重传次数,并结合M/M/1/K排队模型给出了在负载有限的情况下DCF系统性能的理论模型。仿真结果表明,该模型能准确地预测IEEE 802.11b DCF协议的系统性能。     

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/…     

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…     

基于IEEE802.11 DCF的链路预先修复AODV路由协议

基于无线自组织网络中普遍使用的底层通信协议IEEE802.11 DCF,针对广泛应用于无线自组织网络中的路由协议(AODV),提出了一种链路预先修复算法。该算法首先推算了DCF协议中的不稳定传输范围,然后通过MAC层与路由层的跨层协作,在下一跳节点移动在不稳定传输范围时就事先采取相应的路由修复措施。相对于AODV中采用节点周期性地发送HELLO消息来监测邻居节点变化的方法,该算法更为高效及时。仿真结果表明,该算法能够有效的减小端到端时延,保障了投递率。     

Performance analysis of the IEEE 802.11 MAC protocol for wireless LANs

Wireless local area networks (WLANs) are extremely popular being almost everywhere including business, office and home deployments. The IEEE 802.11 protocol is the dominating standard for WLANs. The essential medium access control (MAC) mechanism of 802.11 is called distributed co‐ordination function (DCF). This paper provides a simple and accurate analysis using Markov chain modelling to compute IEEE 802.11 DCF performance, in the absence of hidden stations and transmission errors. This mathematical analysis calculates in addition to the throughput efficiency, the average packet delay, the packet drop probability and the average time to drop a packet for both basic access and RTS/CTS medium access schemes. The derived analysis, which takes into account packet retry limits, is validated by comparison with OPNET simulation results. We demonstrate that a Markov chain model presented in the literature, which also calculates throughput and packet delay by introducing an additional transition state to the Markov chain model, does not appear to model IEEE 802.11 correctly, leading to ambiguous conclusions for its performance. We also carry out an extensive and detailed study on the influence on performance of the initial contention window size (CW), maximum CW size and data rate. Performance results are presented to identify the dependence on the backoff procedure parameters and to give insights on the issues affecting IEEE 802.11 DCF performance. Copyright © 2005 John Wiley & Sons, Ltd.     

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.     

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.     

差错信道下IEEE 802.11 DCF最优帧长分析及信道自适应策略

分析了差错信道下IEEE 802.11 DCF在饱和状态下的吞吐量以及帧长度对吞吐量的影响.研究表明在一定的误码率（BER）下存在最优的帧长使得系统吞吐量最大,并且该最优值与发送节点的数目无关.在此基础上,提出了一种简单的基于BER区间划分的帧长控制的信道自适应发送策略.仿真表明,与固定帧长的发送策略相比较,使用该策略在差错信道下可以有效地提高吞吐量.     

IEEE 802.11 DCF的一种优化退避算法

为了提升无线网络的整体性能,通过IEEE 802.11 MAC(媒体访问控制)层DCF(分布式协调功能)在基本工作模式下所使用的二进制退避算法和CW(竞争窗口)的大小对网络整体性能的影响进行了分析。采用了增大初始 CW、取消信道从忙碌变为空闲后继续退避需要等待的DIFS (分布式帧间间隔)和设置一个中间值作为阀值使得节点发送失败或成功后采用不同的退避算法进行退避这3种措施来优化DCF方式下的退避机制。经 OPNET仿真验证,改进算法能够有效地降低网络接入时延并能提高网络吞吐量。     

Adaptive coordination function for IEEE 802.11 wireless LANs

Multiple access control (MAC) protocols play a significant role in wireless LANs. The IEEE 802.11 MAC protocol specifies two coordination functions that are Distributed Coordination Function (DCF) and Point Coordination Function (PCF). While both DCF and PCF are available in a wireless cell, we propose a novel access mechanism called Adaptive Coordination Function (ACF) to support various classes of traffic. The ACF superframe comprises two periods, one TDMA period designed for real-time traffic and followed by an adaptive period which adaptively employs DCF or PCF to support non-real-time traffic. In this paper, we apply the theory of M/G/1 queues to analyze the performance of adaptive period in terms of queuing delay, end-to-end delay, and saturation throughput. With our analytic model, DCF or PCF can be invoked appropriately according to the number of stations, packet arrival rate, packet payload size, and effective channel bit rate. Analytical results are derived for an extensive throughput and delay performance evaluation of both DCF and PCF.     

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.     

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.     

一种有效的基于变长包的IEEE 802.11系统性能分析方法

本文对DCF的退避过程建立马尔可夫链模型,通过理论分析,估计出了在各个站点运行不同业务、有着不同的包长分布的情况下,系统吞吐量及各个站点占有的网络带宽。在通过仿真工具NS-2进行验证后,取得了较为准确的结果。系统吞吐量及各个站点占用带宽情况的估计,在网络规划、接纳控制、切换等过程中都有非常重要的意义。