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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。 相似文献
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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。 相似文献
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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. 相似文献
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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. 相似文献
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一种最小竞争窗口自适应调整的802.11退避算法 总被引:1,自引:0,他引:1
该文在对原有的IEEE 802.11 DCF研究的基础上,提出了一种基于最小竞争窗口自适应调整的退避算法(Minimum Contention Window Self-adaptive Adjusting, MCWSA)。该算法的思想是每个站点根据网络中当前的时隙利用率和理论上最优时隙利用率进行比较,周期性动态调整自身的最小竞争窗口,以适应不同的网络拥塞状况。仿真表明,该算法提高了IEEE 802.11局域网在拥塞情况下的性能,在饱和吞吐量和时延上都有不同程度的改善。 相似文献
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SCWGF:802.11 DCF竞争窗口增长因子自适应调整算法 总被引:1,自引:1,他引:0
802.11 DCF(Distributed Coordination Function)性能的分析和改进是MAC(Medium Access Control)中一个重要的研究领域.本文在该协议的基础上提出了一种竞争窗口增长因子自适应调整算法—SCWGF(Self-adaptive algorithm of adjusting Contention Window’s Growth Factor),通过理论分析得到不同竞争节点数下竞争窗口增长因子的最优解和最优冲突时间占用率,提出了使用自适应算法使竞争窗口增长因子收敛到最优解,仿真结果表明SCWGF提高了网络的饱和吞吐量. 相似文献
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ZHANG Ye HE Chen JIANG Lingge 《电子学报:英文版》2008,(3):507-512
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. 相似文献
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Chih‐Heng Ke Chih‐Cheng Wei Kawuu W. Lin Jen‐Wen Ding 《International Journal of Communication Systems》2011,24(8):1033-1048
Based on the standardized IEEE 802.11 Distributed Coordination Function (DCF) protocol, this paper proposes a new backoff mechanism, called Smart Exponential‐Threshold‐Linear (SETL) Backoff Mechanism, to enhance the system performance of contention‐based wireless networks. In the IEEE 802.11 DCF scheme, the smaller contention window (CW) will increase the collision probability, but the larger CW will delay the transmission. Hence, in the proposed SETL scheme, a threshold is set to determine the behavior of CW after each transmission. When the CW is smaller than the threshold, the CW of a competing station is exponentially adjusted to lower collision probability. Conversely, if the CW is larger than the threshold, the CW size is tuned linearly to prevent large transmission delay. Through extensive simulations, the results show that the proposed SETL scheme provides a better system throughput and lower collision rate in both light and heavy network loads than the related backoff algorithm schemes, including Binary Exponential Backoff (BEB), Exponential Increase Exponential Decrease (EIED) and Linear Increase Linear Decrease (LILD). Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Yun Li Ke‐Ping Long Wei‐Liang Zhao 《International Journal of Communication Systems》2006,19(9):977-992
Much research has been conducted on saturation throughput of IEEE802.11 DCF, and has led to some improvement. But increasing the successful transmission probability of packet is also important for saving stations' battery energy and decreasing the packet delay. In this paper, we define a new performance parameter, named Product of successful transmission Probability and saturation Throughput (PPT), for 802.11 DCF, which binds successful transmission probability and saturation throughput together. An analysis is given to maximize PPT. An expression of optimal minimum contention windows (CWmin) is obtained analytically for maximizing PPT. For simplicity, we give a name DCF‐PPT to the 802.11 DCF that sets its CWmin according to this expression. The performance of DCF‐PPT is simulated with different stations in terms of saturation throughput, successful transmission probability and PPT. The simulation results indicate that, compared to 802.11 DCF, DCF‐PPT can significantly increase the PPT and successful transmission probability (about 0.95) on condition that the saturation throughput is not decreased. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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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/… 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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Modeling Channel Access Delay and Jitter of IEEE 802.11 DCF 总被引:1,自引:0,他引:1
Yun Li Chonggang Wang Keping Long Weiliang Zhao 《Wireless Personal Communications》2008,47(3):417-440
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.
相似文献
Chonggang WangEmail: |
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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。 相似文献
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Zoran Hadzi-Velkov Boris Spasenovski 《International Journal of Wireless Information Networks》2002,9(3):191-199
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. 相似文献
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R. Jayaparvathy S. Anand S. Dharmaraja S. Srikanth 《International Journal of Communication Systems》2007,20(3):273-296
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. 相似文献
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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 (pd) 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 pd and w, this allows us to configure pd 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. 相似文献