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改进型帧时隙ALOHA防碰撞算法研究 总被引:2,自引:0,他引:2
为进一步提高RFID系统中电子标签防碰撞算法的识别效率,对帧时隙ALOHA防碰撞算法的性能进行分析,提出一种结合精确标签估计和二进制搜索的改进型帧时隙ALOHA算法.将识别过程分为标签估计和标签识别两个阶段,在标签估计算法中引入碰撞概率上、下限参数,并精确估计标签数量对初始帧时隙大小进行优化;在标签识别阶段,利用二进制搜索算法对时隙内的碰撞标签进行快速识别.通过对识别过程进行仿真结果表明:改进的算法改善了防碰撞性能,提高了RFID系统的标签识别效率. 相似文献
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自调整混合树RFID多标签防碰撞算法 总被引:5,自引:0,他引:5
在RFID系统中,阅读器读取标签的效率与解决标签发生碰撞的方法密切相关.目前采用多叉树查询是一种较好的多标签防碰撞方法.它能减少碰撞时隙,再通过额外的查询来减少空闲时隙.但额外的查询也增加了新的开销.本文提出了一个自调整混合树RFID多标签防碰撞算法,该算法根据最高两个碰撞位的特征,在不增加额外查询的条件下,自调整搜索树的叉数,从而避免了一些碰撞时隙和空闲时隙.通过对算法的性能分析和仿真结果可以看到,自调整混合树RFID多标签防碰撞算法具有较少的时间复杂度和通信复杂度,识别效率也明显高于其他多叉树算法. 相似文献
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针对RFID树型防碰撞算法中时隙数多、数据通行量大等问题,提出了一种改进的多叉树防碰撞算法,阅读器准确检测碰撞位并向标签反馈碰撞位信息,标签对阅读器已知的ID位进行屏蔽,把ID号转换成连续碰撞的序列号.阅读器利用屏蔽位信息和标签返回的碰撞位编码信息,对标签进行分层分类搜索.通过对标签ID进行屏蔽,阅读器和标签间仅发送对方不知道的碰撞位信息.该算法减少了碰撞时隙和识别时隙,避免了空闲时隙,减少了阅读器和标签间的数据通信量.理论分析和仿真结果表明,该算法减少了系统的时隙总数和数据通信量,提高了阅读器的识别效率. 相似文献
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射频识别(Radio Frequency IDentification,RFID)技术具有同时识别多个标签的能力.由于标签随机占用信道会使响应信号发生混叠,当大量的标签在读写器感应区域内同时响应势必会引起标签碰撞问题,严重影响了RFID的系统吞吐率.为进一步提高RFID系统吞吐率,在不增加标签端算法复杂度和硬件的条件下,本文提出了预设调整盘存周期的差分门限、时隙前向检测后向预测和二进制散列的方法,协同处理当前时隙和下一个时隙的标签响应情况.利用预设差分门限的方式避免读写器进行浮点运算,同时通过时隙前向检测和后向预测的方法提前判别当前时隙和下一个时隙的标签响应情况,然后快速跳过当前空闲时隙和下一个空闲时隙,并对在当前碰撞时隙和下一个碰撞时隙响应的标签实时进行二进制散列.通过盘存周期调整方式比较、时隙散列方式对比、识别时延与吞吐率比较三个仿真实验,结果显示改进的算法提高了读写器的计算效率,明显减少了无效时隙占用信道的时间,RFID系统吞吐率可提高到52%以上. 相似文献
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新的改进IEEE 802.11 DCF性能的退避机制 总被引:1,自引:1,他引:0
分布式协调功能DCF是IEEE802.11标准最基本的媒体接入方法,它的核心是载波检测多址接入/冲突避免(CSMA/CA)机制,通过退避算法,减少碰撞的概率。提出了一种新的退避机制改进IEEE802.11DCF饱和吞吐量性能,建立了三维马尔可夫链网络模型详细研究分析,同时利用NS2对所提出的机制进行仿真,比较了改进后的802.11DCF饱和吞吐量与原802.11DCF的饱和吞吐量的大小,仿真结果证明了算法的准确有效。 相似文献
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射频识别RFID作为一种重要的物联网终端数据采集技术,系统的吞吐率直接影响着数据采集终端的性能,但目前广泛应用于无源RFID系统的帧时隙类防碰撞算法吞吐率普遍较低.本文着重分析了影响无源RFID帧时隙类ALOHA防碰撞算法性能两类因素:帧长和碰撞时隙的处理方式,通过构建和求解帧长调整和标签碰撞的数学模型,给出了无源RFID帧时隙类ALOHA防碰撞算法的具体优化途径和方案:帧长自适应调整和碰撞实时散列.在此基础上提出了自适应二进制散列帧时隙ALOHA防碰撞算法-ABSFSA.实验结果表明ABSFSA算法在同等条件下可以有效减少无效时隙,明显将RFID系统的吞吐率稳定提高到45%.本文的研究工作为无源RFID帧时隙类防碰撞算法的优化提供了可供参考的数学模型,同时对提升物联网数据采集终端的性能具有一定的应用价值. 相似文献
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为进一步提高射频识别阅读器的标签识别效率,提出一种按需时隙分配高效防碰撞协议.该协议将识别循环分为预约帧时隙阶段和在帧时隙内读取标签两个阶段,通过帧前预约机制消除读取阶段的空闲时隙,采用预约冲突捕获机制有效地减少了读取阶段的碰撞时隙数.在此基础上,通过选择最优预约时隙随机码位数和最优预约时隙数,实现了该防碰撞协议的识别效率最优化,分析了该协议标签电路复杂性,并给出了适用于本协议的标签数估计方法.性能评估表明:该防碰撞协议的平均识别效率达到91.28%,在通信复杂性和识别速度方面明显优于现有典型防碰撞协议. 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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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. 相似文献
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该文提出了一种新的应用于IEEE 802.11e EDCA (Enhanced Distributed Channel Access)中提供QoS(Quality of Service)的方法.这种方法是将几个时隙组合起来构成一个超时隙,每个超时隙的开始分配给不同的业务来进行发包.时隙的分配是根据各种业务的不同优先级来实现的.这种方法可以保证高优先级业务具有较大的吞吐量,较少的MAC延时和较低的丢包率.与802.11e EDCA草案中提出的不同冲突窗口大小的方法相比,这种方法具有可以提高吞吐量,降低丢包率,并能减小站点数目变化对高优先级业务吞吐量的影响等优点.这种新的提供QoS的方法优于不同冲突窗口大小的方法,在IEEE 802.11e EDCA中应用超时隙方法可以大大提高EDCA的性能. 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
15.
In this paper, we introduce a comprehensive packet delay analysis for wireless networks based on IEEE 802.11 Distributed Coordination
Function (DCF). We develop mathematical models that calculate a set of packet delay metrics, namely a) the average packet
delay for successfully transmitted packets, b) the average packet delay of successfully transmitted packets experiencing a
specific number of collisions, c) the average packet drop time, d) the delay jitter and e) the delay distribution by computing
the probability of a packet to be successfully transmitted experiencing delay time lower than a given value. All the developed
models are based on calculating station’s delay time at the transmission slot(s) plus the average time that station defers
at backoff slots before successful transmission. The mathematical models are simple, computationally fast and can be used
to build admission control algorithms. Simulation results show that our proposed mathematical analysis is highly accurate. 相似文献
16.
Performance Analysis of IEEE 802.11 DCF in Imperfect Channels 总被引:1,自引:0,他引:1
《Vehicular Technology, IEEE Transactions on》2006,55(5):1648-1656
IEEE 802.11 is the most important standard for wireless local area networks (WLANs). In IEEE 802.11, the fundamental medium access control (MAC) scheme is the distributed coordination function (DCF). To understand the performance of WLANs, it is important to analyze IEEE 802.11 DCF. Recently, several analytical models have been proposed to evaluate the performance of DCF under different incoming traffic conditions. However, to the best of the authors' knowledge, there is no accurate model that takes into account both the incoming traffic loads and the effect of imperfect wireless channels, in which unsuccessful packet delivery may occur due to bit transmission errors. In this paper, the authors address this issue and provide an analytical model to evaluate the performance of DCF in imperfect wireless channels. The authors consider the impact of different factors together, including the binary exponential backoff mechanism in DCF, various incoming traffic loads, distribution of incoming packet size, queueing system at the MAC layer, and the imperfect wireless channels, which has never been done before. Extensive simulation and analysis results show that the proposed analytical model can accurately predict the delay and throughput performance of IEEE 802.11 DCF under different channel and traffic conditions. 相似文献
17.
P. Chatzimisios A. C. Boucouvalas V. Vitsas 《International Journal of Communication Systems》2005,18(6):545-569
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. 相似文献
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Mohand Yazid Louiza Bouallouche-Medjkoune Djamil Aïssani Nassim Amrouche Kamel Bakli 《Wireless Personal Communications》2014,77(1):477-506
The mathematical modeling and performance evaluation of the IEEE 802.11 network in all its various extensions (802.11b, 802.11a, 802.11g, 802.11e, 802.11n, etc.) have already been widely explored over the past years. However, the Packet Fragmentation Mechanism (PFM), which is proposed by the IEEE work group to enhance the MAC sub-layer of the IEEE 802.11 standard in an error-prone channel, has been missed in the available literature. Yet, the PFM is the only existing solution to reduce the influence of bit error rate and the length of data packets on the packet error rate, and consequently on the performances of IEEE 802.11 networks. In this paper, we propose a new three-dimensional Markov chain in order to model, for the first time in the literature, the PFM in both Basic and RTS/CTS access methods of the IEEE 802.11b DCF network under imperfect channel and finite load conditions. Then, we develop mathematical models to derive a variety of performance metrics, such as: the overall throughput, the average packet delay successfully transmitted, the average packet drop time, the delay jitter and the packet delay distribution. Performance analysis of applying PFM on both Basic and RTS/CTS access methods of the IEEE 802.11b DCF network under imperfect channel and finite load conditions shows original results and leads to new conclusions that could not be intuitively expected. 相似文献
20.
According to the amendment 5 of the IEEE 802.11 standard, 802.11n still uses the distributed coordination function (DCF) access method as mandatory function in access points and wireless stations (essentially to assure compatibility with previous 802.11 versions). This article provides an accurate two dimensional Markov chain model to investigate the throughput performance of IEEE 802.11n networks when frame aggregation and block acknowledgements (Block-ACK) schemes are adopted. Our proposed model considered packet loss either from collisions or channel errors. Further, it took anomalous slots and the freezing of backoff counter into account. The contribution of this work was the analysis of the DCF performance under error-prone channels considering both 802.11n MAC schemes and the anomalous slot in the backoff process. To validate the accuracy of our proposed model, we compared its mathematical simulation results with those obtained using the 802.11n DCF in the network simulator (NS-2) and with other analytical models investigating the performance of 802.11n DCF. Simulation results proved the accuracy of our model. 相似文献