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介质访问控制(MAC)协议的物理载波侦听机制是一种减少冲突的有效方法。同时,载波侦听阈值的大小对网络性能也有很大影响。由于无线自组织网络物理层可具有多种速率,而MAC层中的发送速率与物理层速率的不匹配,会导致网络拥塞和网络性能下降。在分析物理层速率和载波侦听阈值之间关系的基础上,提出一个选择与多速率相匹配的载波侦听阈值算法,最后基于物理层的最理想速率,对MAC层和物理层信道利用率进行比较,再通过竞争窗口来自适应控制MAC层的发送速率来提高网络性能。仿真结果表明,该机制在吞吐量和延迟方面要优于802.11DCF,在吞吐量方面提升了47.66%,在延迟方面降低了33.18%。 相似文献
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针对现有的太赫兹无线个域网络中太赫兹辅助波束赋形媒体访问控制(MAC)协议(TAB-MAC)存在数据传输时延较大以及信道利用率低问题,提出了一种高效快速的太赫兹无线个域网双信道MAC协议(EF-MAC)。通过目的节点向源节点发送测试帧机制来减少一个确认帧,从而减少控制开销和测试时延;采用自适应取消节点位置信息的收发机制,源或目的节点通过之前的请求发送帧/允许发送帧(RTS/CTS)帧交互过程已获得对方节点的位置信息且对方节点的位置没有发生改变,可以省去RTS或CTS中的位置信息,减少控制开销。理论分析与仿真结果表明,与TAB-MAC协议相比,所提协议能够有效减小数据传输时延,提高网络吞吐量。 相似文献
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无线Mesh网络中使用双收发器的多信道MAC协议研究 总被引:2,自引:0,他引:2
在无线Mesh网络中,当底层有多个可用的物理信道时,必须设计高效的媒体访问控制协议(MAC)才能充分利用所有可用信道,克服多信道的隐终端和显终端问题。三类多信道MAC协议都只使用了两个无线收发器,却能够在保持经济性的同时最大限度地利用多个信道,并解决多信道环境下广播消息发送和信道切换等问题。分析比较表明,该MAC协议能够在一定程度上利用多个信道增加网络的有效吞吐量,但在保证网络负载均衡上还存在不足,需要进一步研究。 相似文献
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在无线局域网(WLANs)中,介质访问控制(MAC)协议的设计是一个核心的问题。MAC协议应该满足较高的吞吐量和较好的公平性等要求。根据802.11分布式协同函数(DCF),提出了一种新的高效的竞争窗口(CW)处理机制,称作自适应倍乘增加倍乘减小算法(ADD)。该算法的基本思想如下:每个站点在成功地连续发送n个数据包后,其MAC层的竞争窗口减小为原值的一半,而且n的值根据接入节点(AP)的瞬时流量自适应地调节。大量仿真实验表明:该算法可以通过有效地降低站点之间的冲突概率,来增加系统整体的吞吐量,同时增加不同站点之间的公平性。 相似文献
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水声传感网MAC协议综述 总被引:1,自引:0,他引:1
海洋在人类发展中扮演着越来越重要的角色。水下通信技术作为人类认识海洋的重要手段,成为研究界的热点与难点。由于水下通信技术有不同于陆地无线通信的信道特点和性能要求,传统无线通信MAC(medium access controD协议难以直接应用于水声通信,因此相继提出针对各种应用场景的水声MAC协议。在简述水声传感网(Undcrwatcr Acoustic Sensor Nctwork,UWASN)特点和MAC协议设计准则后,根据信道获取方式将当前典型协议分为基于竟争和基于调度两大类。根据冲突处置方式进一步将基于竞争的协议分为随机多址和冲突避免,根据信道分配的动态性将基于调度的协议分为动态分配和静态分配。在此分类基础上,描述了近期出现的典型协议的设计思想、主要机制,并比较了协议在能耗、信道利用、吞吐量等方面的差异,最后指出提高MAC协议性能的发展方向。 相似文献
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在无线传感器网络中,MAC协议决定着网络的信道分配,对网络的性能有很重要的影响。目前已研究出多种S-MAC协议,其中S-MAC协议是一种典型的无线传感器网络MAC协议,但此协议存在一定缺陷,无法更好地适应传感器网Jj络多变的特点。针对该问题,在S-MAC协议的基础上,结合了自适应退避窗口和根据节点队列长度预测流量的思想,提出了一种新的协议-Q-MAC协议,并达到了较为理想的预测效果。经NS2仿真验证,此协议在平均延迟、吞吐量、能量消耗方面较S-MAC协议有了显著提高。 相似文献
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S-MAC协议设计的主要目标是减少能量消耗。该协议具有良好的扩展性,不要求严格的时间同步,但它也存在着节点活动时间无法根据通信负载动态变化和节点休眠带来的延迟问题。提出一种基于节点任务活动状态感知的MAC协议,通过收集节点自身和相邻节点的任务活动状态来估算无线传感器网络的网络负载,并根据网络负载来确定节点进行信道访问的概率,以此来提高能量效率和吞吐量。仿真结果表明:提出的改进方法可以减少能量消耗,并通过消除不必要的碰撞来提高网络的吞吐量。 相似文献
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N. Sai Shankar 《Journal of Scheduling》2004,7(2):149-167
Bidirectional Cable TV networks using hybrid fiber coaxial (HFC) systems are good examples of broadcast environments where a contention resolution algorithm is needed in order to allocate the multiaccess medium among various customers. The medium access control (MAC) scheme, proposed by DAVIC/DVB, IEEE 802.14 and DOCSIS for the upstream channel of HFC access networks is based on a mixable contention-based/contentionless time slot assignment. Contention-less (CL) slots are assigned by the head-end (HE) to end stations according to a reservation scheme. Contention-based slots (CB) are randomly accessed by active terminals without any prelimanry allocation and so collisions may occur. To resolve contention the contention tree algorithm has been widely accepted by the DVB/DAVIC, IEEE 802.14 and DOCSIS standards for MAC because of higher throughput and lower access delay. In this paper we propose a simple modification to the existing protocol and analyze its performance. We propose to have one slot in the frame exclusively reserved for the new arrivals that wish to access the channel capacity using contention resolution and atleast one more slot reserved for resolving their contention if there was a contention in the arrival slot. This assumption simplifies the protocol to a queuing mechanism and we use the results of the queue to analyze the protocol. The queuing analysis method is used to determine the throughput of the channel and waiting times of the arbitrary customers. Furthermore, we present numerical results and compare that with simulations. 相似文献
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In this paper, we present CCM-MAC, a cooperative CDMA-based multi-channel medium access control (MAC) protocol for mobile ad hoc networks (MANETs) in which each node has one half-duplex transceiver. The protocol mitigates the multi-channel hidden and exposed terminal problems by using information about channel usage gleaned from overhearing (cooperating) neighbours. By accounting for the multiple access interference, CCM-MAC also addresses the near-far problem of CDMA in MANETs enabling concurrent transmissions on each channel. We provide an analysis of the maximum throughput of CCM-MAC and validate it through simulation in Matlab. We also compare the throughput it achieves to IEEE 802.11, a multi-channel MAC protocol, and a CDMA-based MAC protocol. 相似文献
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Cognitive radios have a great potential to improve spectrum utilization by enabling dynamic spectrum access. A key challenge in operating these radios is how to implement an efficient medium access control (MAC) mechanism that adaptively and efficiently allocates transmission powers and spectrum according to the surrounding environment. In this work, we propose a distributed MAC protocol for operating spectrum-agile radios in a multi-hop ad hoc network. Our protocol is unique in that it exploits the “dual-receive” capability of radios, which is used to overcome channel access problems that are common to multi-channel designs. We conduct theoretical analysis of the protocol and study its performance via simulations. To further improve the system throughput, we propose a framework for joint adaptive load and medium access controls. Simulation results show that the proposed scheme achieves more than 90% of the maximum (global) system throughput that is achieved at saturation, while guaranteeing low collision rates. 相似文献
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无线传感器网络多信道节能信道接入控制协议 总被引:3,自引:0,他引:3
在无线传感器网络MAC这一广阔的研究领域已经开展了很多研究工作,但迄今对能量节省并没有很好的解决方案,一般都以牺牲其他性能来降低能耗的.多信道节能MAC协议结合传感器网络对信道接入控制的要求,综合提高了网络性能,通过ns-2仿真,验证了本协议在能量节省、信道公平性以及网络吞吐量等方面的性能改善. 相似文献
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Mohammed Abd-ElnabyAuthor Vitae M.R.M. RizkAuthor Vitae 《Computers & Electrical Engineering》2011,37(1):115-125
Efficient medium access control (MAC) protocol should be able to provide high throughput performance and efficient share of the medium. In this paper, a new contention-based MAC protocol based on adaptive fuzzy controlled sliding backoff interval is proposed to maximize the channel throughput and improve the fairness of random access channels. In the proposed protocol, every node that experiences packet collisions increases its sliding backoff interval (SB) range by a forward sliding factor (FSF). In case of successful transmission the node decreases its SB range by a backward sliding factor (BSF). Forward and backward sliding factors are controlled by the channel offered traffic using a fuzzy controller. Furthermore, the operation of the proposed backoff algorithm does not depend on the knowledge of the number of active nodes. A computer simulation is developed using MATLAB to evaluate the performance of the proposed algorithm and compare it with other backoff schemes. Simulation results show that the proposed algorithm significantly outperforms other backoff schemes, such as binary exponential backoff (BEB) and the fast collision resolution (FCR) scheme. It provides a significant efficient fair sharing performance improvement which converges to the ideal fairness performance while providing high throughput performance. 相似文献