共查询到19条相似文献,搜索用时 187 毫秒
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本文针对无线局域网中MAC层Qos支持技术进行了研究,在分析了现有的EDCF退避机制的静态参数设置方法的基础上,提出结合网络负载状况动态调节不同优先级业务的竞争窗口和退避时间,改变不同优先级业务的信道接入方式的方法。仿真结果表明,动态调节法相较于静态参数法在网络吞吐量、时延、碰撞率方面都有更好的表现。 相似文献
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该文利用二维Markov链分析方法,提出了一种新的IEEE802.11e EDCA网络分析模型,该模型引入了空闲状态和不同接入等级的仲裁帧间隔(AIFS)的使用;利用Markov链状态转移图的Z域信号传递函数推导了MAC层平均服务时间的概率分布;结合M/G/1/K排队模型分析了增强分布式信道接入(EDCA)在非饱和和饱和负载下的性能。经过访真实验结果与数值分析结果的对比,验证了分析模型的准确性。分析结果表明:EDCA接入机制只为不同优先级业务提供QoS区分;不同优先级业务信道接入的不公平性是EDCA接入机制的特点。 相似文献
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随着通信系统的不断发展,对融合地面系统的天地一体化网络的研究越来越多,而卫星通信系统中,由于卫星高速移动等特性,不可避免需要对呼叫的接入切换进行研究。针对天地一体化信息网络需要支持多场景多业务情况下的通信需求,考虑不同呼叫优先级不同,对多优先级的多种呼叫业务进行考虑。根据信道预留的思想,对不同优先级接入与切换呼叫设定不同的可用信道数,优先级越高的呼叫,为其留更多的可用信道以确保其接入信道成功。同时,由于动态信道预留较固定信道预留能够更好地利用信道资源,最终考虑多优先级下的动态信道预留策略。对多优先级动态信道预留与多优先级固定信道预留策略进行仿真验证,发现动态预留方案得到的系统服务质量更好。对于单一策略,发现优先级越高的用户接入与切换呼叫接入信道失败率更低。 相似文献
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在共享媒体的通信系统中,队列调度的公平性是很重要的。该文在研究了IEEE WLAN已有的各种队列调度算法的基础上,提出了一种预测式公平队列调度算法 (Predict Fair Queuing, PFQ),并结合IEEE 802.11e的EDCF(Enhanced Distributed Coordination Function)机制提出一种基于PFQ的新的MAC层协议P-EDCF(PFQ-based EDCF)。该协议通过引进PFQ算法来修改EDCF的优先级控制方式,提供一种公平、高效的接入机制。仿真结果表明,该机制很好地改善了EDCF的性能,为各种类型业务提供了公平的服务。 相似文献
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针对航空Ad Hoc网络在高负载下的低时延信道接入问题,提出一种优先级与公平性协作的多信道MAC协议(PBLL/HL)。在多信道检测统计基础上加以改进,结合优先级机制,在高负载网络中适时截流低优先级业务,优化网络流量,保证高优先级业务低时延发送;设计公平性优先级阈值与冲突退避窗口算法(PCA),减小低优先级业务接入时延。仿真结果表明,PBLL/HL能够在高负载网络有效控制信道接入,维持良好的网络流量,降低网络平均接入时延(低优先级业务时延过载时降低10%以上),稳定高负载网络吞吐量(最大吞吐量88.1%,过载时吞吐量下滑平缓),解决了航空数据链高业务量带来的高时延和网络拥塞。 相似文献
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One of the most important functions in IEEE 802.11e is enhanced distributed coordination function (EDCF). EDCF is an enhanced version of IEEE 802.11 distributed coordination function (DCF) which provides a priority scheme by differentiating the inter‐frame space and the initial window size. We proposed a modified Markov chain model to study the EDCF priority scheme. We have theoretically analyzed the saturation throughput and delay by using the modified Markov chain model in non‐ideal channel scenario. We also have compared it with the Markov chain model that exists under ideal channel scenario. Simulations are also conducted to validate analytical results. Our study shows that the modified model under ideal channel scenario is better than that in channel error scenario. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Kenan Xu Quanhong Wang Hossam Hassanein 《International Journal of Communication Systems》2005,18(7):619-637
This paper proposes a multi‐dimensional Markov model to analyse the performance of the IEEE 802.11e EDCF MAC protocol. Based on this model, we present extensive performance evaluation in terms of throughput, throughput ratios, and access delay of flows of distinct priorities under RTS/CTS mode. We also provide quantitative analysis of the impact of prioritized parameters, i.e. Arbitration InterFrame Space (AIFS), Contention Window (CW) on Quality of Service (QoS) differentiation. The accuracy of the proposed model is verified by means of comparing the numerical results obtained from both analytical model and simulations. Our research can be used as a guideline for the prediction of how flows belonging to a certain Traffic Category (TC) perform with their TC‐specific parameters, as well as designing EDCF‐based WLANs and tuning the parameters to achieve the desirable differentiated QoS objectives. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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In IEEE 802.11e Enhanced Distributed Coordinator Function (EDCF) (In the recently approved IEEE 802.11e standard, EDCF is
renamed to enhanced distributed channel access (EDCA). Throughout this paper, we use EDCF for consistency with early work
in the literature.), per-flow service differentiation is achieved by maintaining separate queues for different traffic categories
(TCs). However, due to its static Quality of Service (QoS) parameter setting, EDCF does not perform adequately under high
traffic load (Romdhani et al., Proceedings of IEEE wireless communications and networking conference, 2003). We present an
extended performance model of EDCF and analyze conditions for network getting overloaded. With this extended model, we show
that the overall throughput of a network can be improved by changing the distribution of the number of active stations (an
active station is one that has a pending packet to be sent) over a set of TCs. Hence, we propose to dynamically re-allocate
flow priorities evenly in order to maintain high system performance while providing QoS guarantee for individual real-time
flows. Our scheme has several interesting features: (1) performance of EDCF is improved; (2) low priority flows are not starved
under high traffic load; (3) misuse of priority (misuse of priority means that a flow requests much higher priority than necessary)
can be easily handled. Simulations are conducted for both infrastructure-based and Ad hoc models. Results show that dynamic
priority re-allocation does not decrease throughput of real-time flows under low to medium loads, while considerable improvement
over EDCF is obtained even under high loads, making it easy to support multimedia applications. 相似文献
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在Malli提出的AEDCF机制的基础上,把基于信道条件的P因子引入到EDCF机制中去,提出了一种动态自适应EDCF(DAEDCF)机制。在DAEDCF机制中,退避时间和竞争窗口的更新依赖于P因子,在信道条件好的情况下,减少了时延,提高了信道利用率,在信道条件糟糕时,减小了碰撞几率。提高了系统的性能。通过仿真可以看到,DAEDCF机制在高负载下,进一步提高了各优先级。特别是中、低优先级业务流的性能。和AEDCF机制相比,在信道负载达到80%时.Video流的吞吐量提高了2%,平均时延降低了25%,Background流的吞吐量提高了14%。平均时延降低了20%。 相似文献
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Enhancing channel utilization by improving media access coordination in wireless local area networks
Distributed coordination function (DCF) is the basis protocol for IEEE 802.11 standard wireless local area networks. It is based on carrier sense multiple access with collision avoidance (CSMA/CA) mechanism. DCF uses backoff process to avoid collisions on the wireless channel. The main drawback with this process is that packets have to spend time in the backoff process which is an additional overhead in their transmission time. The channel is rendered idle when all the stations defer their transmissions due to their backoff process. Therefore, the channel utilization and the total throughput on the channel can be improved by reducing the average time spent by the packets in the backoff process. In this paper, we propose a new media access coordination function called proposed media access protocol (PMAP) that will improve the channel utilization for successful packet transmission and therefore, the total achievable throughput. In addition, we propose an analytical model for PMAP under saturated conditions. We use this model to analyze the performance of PMAP under saturated conditions. To substantiate the effectiveness of our model, we have verified the model by simulating PMAP in NS‐2. Simulation and analytical results show that under saturated conditions, PMAP shows profound improvement in the throughput performance compared to DCF. In addition, the throughput performance of PMAP under unsaturated conditions is presented. We have also presented the delay performance of PMAP and DCF through simulation in both saturated and unsaturated conditions. Simulation results show that the average delay experienced by the packets is less in PMAP compared to DCF. Further, the variance in the packet delay is same for both PMAP and DCF protocols under unsaturated conditions. From the performance results obtained for PMAP under both saturated and unsaturated conditions, it can be concluded that PMAP is superior in performance compared to DCF. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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LiXiaohui KouWeidong LiuNai'an YiKechu 《电子科学学刊(英文版)》2005,22(4):416-421
Based on the Distributed Coordination Function (DCF) and the Enhanced DCF (EDCF) mechanisms in IEEE 802.11 and 802.11e, a novel backoff scheme for Wireless Local Area Network (WLAN) is proposed. The scheme is to solve the problem of the packet loss and the decrease of performance due to the increasing Contention Window (CW) when there are continuous collisions. In the proposed scheme, the CW of the packet will change dynamically with different delay for the different traffics. Mathematic formulas are presented to indicate the relationship between the CW and the delay character. The performance of the new scheme is also discussed with simulation results. The results show that it helps WLAN system handle multimedia simultaneously. 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
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IEEE 802.11e enhanced distributed channel access (EDCA) is a distributed medium access scheme based on carrier sense multiple access with collision avoidance (CSMA/CA) protocol. In this paper, a model-based admission control (MBAC) scheme that performs real-timely at medium access control (MAC) layer is proposed for the decision of accepting or rejecting requests for adding traffic streams to an IEEE 802.11e EDCA wireless local area network (WLAN). The admission control strategy is implemented in access point (AP), which employs collision probability and access delay measures from active flows to estimate throughput and packet delay of each traffic class by the proposed unsaturation analytical model. Simulation results prove accuracy of the proposed analytical model and effectiveness of MBAC scheme. 相似文献
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During the past few years the widespread use of the wireless local area networks (WLANs) communication technique is one of the most popular technologies in data telecommunications and networking. With the increasing variety of multimedia applications, it is needed to develop a mechanism for the quality of service (QoS) to support different types of traffic. The IEEE 802.11 protocol has achieved worldwide acceptance with WLANs with minimum management and maintenance costs. However, IEEE 802.11 can only provide a best effort service and does not support the QoS. In this paper, we pay attention to the enhanced distributed coordination function (EDCF) of WLANs. First, we modify the Ziouva and Antonakopoulous’s (ZA’s) model and then extend the model to support EDCF. We study the behavior of the station within a Markov chain model, and present a more accurate analysis of the EDCF and also study the saturation throughput when the maximum load that the system can support is reached. The numerical results show that the modified model has a better performance than the ZA’s model under an ideal channel scenario. 相似文献