一种无线传感器网络MAC协议优化算法

在无线传感器网络中,各节点采集的信息以多跳的方式传送到汇聚点.从各节点到汇聚点形成一棵以汇聚点为根的传输树.文中在对无线传感器网络传输特点分析的基础上,剖析了基于CSMA/CA(载波多路监听/冲突避免)的MAC协议在树状结构无线传感器网络中的弊端,提出了一种基于CSMA/CA的MAC协议优化算法.算法基于节点在传输树中的位置信息调整其MAC信道接入分配,将CSMA/CA采用的各节点均等竞争信道的方法优化为各节点依据在传输树中的位置情况竞争信道的方式,这一优化提高了节点公平性,使MAC信道接入分配与树状结构的无线传感器网络传输特点相契合,解决了基于CSMA/CA的MAC协议与树状结构无线传感器网络不匹配的问题,从而减少了信道资源浪费,提高了网络传输效率,降低了能耗.实验结果表明该算法在网络丢包率、吞吐量和能耗方面的性能均有较大改进.     

基于预约调度的无线传感器网络的MAC协议*

提出了一种基于预约调度的用于无线传感器网络的MAC协议--SSMAC.该协议采用分布式竞争接入和预约调度发送,提供高能量效率的信道接入和支持QoS业务的传输,较好地解决了隐藏终端和暴露终端问题.仿真结果表明SSMAC协议在保持节能的同时,在降低媒体接入时延、提高报文投递成功率和提供QoS保障上较TRAMA协议性能有很大的提高.     

一种应用于分布式网络的新型私有多信道UWB MAC协议设计

目前,单信道MAC协议在网络负载较重时的冲突和退避,造成信道带宽浪费而使得协议效率不高.本文主要针对UWB应用在无线个域网络中的特定场景,提出了一种新的应用于分布式网络的私有多信道UWB MAC协议,既可以解决隐藏终端和暴露终端问题,又可以有效地分配信道资源,提高网络性能.     

CB-MAC：低延时可靠传输的无线传感器网络MAC协议

针对无线传感器网络中周期性睡眠唤醒调度类MAC协议的延时问题，通过对多跳网络环境中端到端的数据传输延时的分析，提出了一种新型的能快速转发的无线传感器网络MAC协议CB-MAC（Cut-throughB-MAC）。CB—MAC消除了两次传输之间的等待延时，实现了数据的多跳连续转发。协议采用RTS-CTS机制实现了链路层的可靠传输，同时解决了加入控制报文而带来报文开销相对较大的问题。模拟结果表明，在多跳通信下，CS-MAC在报文平均延迟和能耗方面的性能都有较大提高。     

一种无线多媒体传感器网络分区链路调度算法

链路干扰是无线多媒体传感器网络实现大容量、实时、可靠传输的主要困难。为提高多跳传输模式下无线网络性能,基于MAC层的调度算法得到了广泛关注。调度算法为每条链路分配合理的传输时槽,降低了冲突和重传次数,能显著提高网络传输性能。但随着网络规模的增大,无论是集中式还是分布式调度算法,都存在调度开销增大和性能降低的问题。针对这一问题,根据节点分布密度和承载网络流量大小,将网络划分为密集区域和稀疏区域。稀疏区域的节点传输冲突较小,直接采用CSMA的协议。密集区域的节点传输冲突大,采用基于队列长度的分布式调度。分区调度能够有效降低网络规模扩大导致的调度算法复杂性增大的问题。仿真实验表明,分区调度算法无论是在队列长度,还是在延时性能上,较传统算法有明显改善。     

CB-MAC:低延时可靠传输的无线传感器网络MAC协议

针对无线传感器网络中周期性睡眠唤醒调度类MAC协议的延时问题,通过对多跳网络环境中端到端的数据传输延时的分析,提出了一种新型的能快速转发的无线传感器网络MAC协议CB-MAC(Cut-through B-MAC).CB-MAC消除了两次传输之间的等待延时,实现了数据的多跳连续转发.协议采用RTS-CTS机制实现了链路层的可靠传输,同时解决了加入控制报文而带来报文开销相对较大的问题.模拟结果表明,在多跳通信下,CS-MAC在报文平均延迟和能耗方面的性能都有较大提高.     

一种区分的CSMA无线网络调度算法研究

CSMA(Carrier Sensing Multiple Access)算法具有分布式实现的优点,在IEEE802.11WiFi中已经获得了应用,在无线Mesh网络中也有实践价值.本研究以无线网络时隙系统为模型,针对队列积压长度较小的链路可能出现传输超时的情况,进行区分的CSMA调度,为小于权重门限值的链路提供了一定的优先级.仿真显示在系统负载不是很大的情况下,这种区分对待的调度方式在用户时延公平性保证上得到了改善.     

传感器网络通信延迟的实时预测

针对使用CSMA/CA通信机制的无线传感器网络提出一种通信延迟估计算法。利用链路质量具有时间和空间相关性的特点建立组合的链路模型,预测链路可靠性,使用简化的冲突概率模型预测信道竞争延迟,结合预测的链路可靠性得到通信延迟。分析了算法的开销,在ns2模拟器上对信道竞争延迟预测算法进行了模拟,结果表明预测算法能够比较准确地预测网络的竞争延迟。     

带碰撞避免机制的多址接入协议能量效率研究

研究了在自组织网络环境下CSMA/CA协议的能量消耗性能,并与传统的CSMA协议能耗性能进行比较.阐述了自组织网络中的隐藏终端和暴露终端问题,并分析CSMA/CA协议相对传统CSMA协议对该问题进行的改进.仿真结果表明,相对非坚持CSMA协议,CSMA/CA协议能够获得的能量效率更高,并且对网络负载的敏感性更低,在网络负载较高时也具有较高的能量效率.     

对IEEE 802.11 MAC层协议公平性改进的研究

Ad Hoc网络中基于IEEE 802.11的MAC层协议采用CSMA/CA机制,通过侦听只能获取一跳范围内节点的信息,存在隐终端问题,影响了网络流调度的公平性.文中对IEEE 802.11提出了一种修改方案,该方案通过邻居结点间的信息交换,使网络中每个节点具有其二跳范围内所有结点的信息,以发现网络中的隐终端,提高网络流调度的公平性.对比仿真实验结果表明,修改后的IEEE 802.11与原协议的网络吞吐量基本相当,但具有更好的公平性.     

认知无线电网络分布式多信道MAC协议*

在认知无线电网络中,MAC协议用于信道感知、选择和接入控制。以单网卡多信道MAC（MMAC）协议为基础,依据IEEE 802.22标准定义的静默期管理的两阶段感知策略,提出一种认知无线电网络分布式多信道MAC（CR-MMAC）协议。将两阶段感知机制和分布式协商融入MMAC协议,利用空闲频谱进行数据传输,并在MMAC协议ATIM窗的数据信道协商阶段引入预约机制,以避免选择同一信道的认知节点对在后续数据传输阶段再利用CSMA/CA造成的竞争碰撞。仿真对比分析表明,CR-MMAC协议能提高网络吞吐量、降低通信时     

A CSMA/CD compatible MAC for real-time transmissions based on varying collision intervals

This paper suggests a CSMA/CD compatible MAC protocol for real-time transmissions in a shared Home or Small Office Local Area Network. The new MAC is based on the distributed assignment of special TAG numbers to the stations transmitting real-time traffic. These TAG numbers determine a Round Robin order of transmissions among the real-time stations. They also help in resolving collisions among real time stations by setting the length of the Jam signal, transmitted in case of a collision, to be a function of the TAG number. In a collision the station with the highest TAG number, and so with the longest Jam, is persisting with its Jam transmission for the longest until all the other stations defer. Thus, the collision terminates and the longest persisting station can transmit its packet successfully. The new protocol enables stations implementing the IEEE 802.3 MAC standard to transmit on the same network with stations implementing the new protocol. After introducing the protocol, we compute an upper bound on the access delay that the protocol guarantees and prove the correctness of the distributed TAG assignment procedure. Finally, we simulate the protocol in a network consisting stations implementing the new protocol together with stations implementing the standard IEEE 802.3 MAC. We show that the access delays of the stations transmitting real-time traffic are indeed bounded as predicted.     

Enhanced MAC protocol to support multimedia traffic in cognitive wireless mesh networks

With the advanced physical layer techniques such as multiple-input and multiple-output (MIMO) and orthogonal frequency-division multiplexing (OFDM), transmission real-time 2D/3D contents and applications becomes more and more necessary in wireless networks for the amazing growing in demand of customers. However, the low efficiency of medium access control (MAC) protocol degrades the performance of real-time traffic greatly in multihop, wireless and mobile environment. Focusing on supporting real-time multimedia traffic in cognitive wireless mesh networks (WMNs), an enhanced MAC protocol is proposed. And the contribution of this paper is twofold: (1) An efficient carrier sense multiple access with collision avoidance (CSMA/CA) compatible time division multiple access (TDMA)-like MAC protocol called T-MAC is proposed, which aims to improve the system performance by allocating more channel access time in centralized manner and decreasing overhead. (2) An optimal adaptive scheduling scheme is proposed to support real-time multimedia applications and guarantee QoS for different priority traffic, which aims to find the optimized schedule among all possible sequences of concurrent transmissions by minimizing the occupied resources. Detailed simulation results and comparison with IEEE 802.11e MAC scheme show that the proposed T-MAC can effectively improve quality of service (QoS) for multimedia traffic in terms of throughput, end-to-end delay and packet loss rate, which also manifests that T-MAC is an efficient multimedia applications transmission scheme for mobile terminals and MAPs in cognitive WMNs.     

一种新的竞争与分配相结合的MAC协议

针对IEEE 802.11在高竞争下吞吐量低,以及TDMA协议在低负载下吞吐量低的问题,提出了一种新的TDMA MAC协议：Q-TDMA。结合TDMA协议可以保证节点在每个周期内有一个发送机会,而同步CSMA/CA机制可以解决隐藏终端和暴露终端的问题,Q-TDMA协议要求节点根据本身的队列长度来竞争复用时隙。仿真实验结果表明,Q-TDMA提高了网络吞吐量,降低了端到端的延迟。     

基于队列长度的自适应占空比MAC协议

由于无线传感器网络中设备电池能量有限,实现能量高效性是其主要考虑的问题。众所周知优秀的数据传输协议对降低能耗,延长网络生命周期有重要意义。而在基于竞争的MAC协议中,空闲监听是主要能量消耗来源,所以通常设计较低占空比的MAC协议来减少空闲监听时间。但是如果占空比过小,使得网络中所有数据传输集中在较短时间内,会导致节点无法完成所需要的通信。所以选择合适的节点占空比,对于资源受限的网络来说是一种很重要的节能方法。文中提出了一种新型的异步MAC协议QL-MAC,节点利用CSMA争用信道,发送一系列短的信标包唤醒目标节点,采用虚拟载波监听防止串听。不同于其他改变接收节点的方法,该协议从发送节点来考虑,可以根据缓冲区队列长度判断该网络负载,从而自适应调整节点的占空比,使节点及时发送数据,减少时延,并告知接收节点做出相应改变,进一步节省能量。在OMNET++上实现了QL-MAC协议,仿真结果表明QL-MAC协议展现了良好的时延和能量有效性。     

基于CSMA/CD的改进调度算法研究

针对共享式网络中采用CSMA/CD(带有冲突检测的载波侦听多路存取)的通信技术易出现时延的缺点,提出改进的预先呼叫的CSMA/CD调度算法,根据矿井监控系统的特点,实现矿井监控系统中分站节点输出调度.算法的核心是将分站节点编号分组,各组分配载波监听信道闲次数,按照组呼叫输出形式,组内载波侦听到闲的次数满足预先设定的次数时发送,否则不发送,在监控主机接收到上一组的组内倒数第二个信息时,向下一组发送信息,使下一组处于载波侦听状态.实验表明改进的CSMA/CD调度算法解决了CSMA/CD算法存在的信道争用和信息碰撞造成的时延且影响通信实时性的问题.     

认知车载网中基于TDMA/CSMA的混合多信道MAC协议研究

在传统车载自组网(Vehicular Ad Hoc Network, VANET)中采用认知无线电(Cognitive Radio, CR)技术可以解决无线电频谱资源短缺的问题,该技术形成了新兴的认知车载网络(CR-VANET),其关键技术之一是设计高效可靠的介质访问控制(Medium Access Control, MAC)协议。MAC协议在很大程度上影响着车载移动环境的吞吐量,丢包率和传输时延等性能,基于认知车载网中MAC协议的要求,提出了一种TDMA与CSMA相结合的多信道MAC协议(CRTC-MAC)。在固定时隙分配时采用基于无竞争的TDMA访问策略,在动态时隙分配时采用基于竞争的CSMA接入方案,并在此基础之上对传统的TDMA和CSMA访问方式进行了改进。性能分析和仿真结果表明,所提出的MAC协议能有效降低节点间数据包传输时所产生的碰撞,改善网络性能。     

Fuzzy logic-based performance improvement on MAC layer in wireless local area networks

There are many studies that have been done to improve the quality of service of wireless local area networks (WLANs). Institute of Electrical and Electronic Engineers (IEEE) WLAN are based on IEEE 802.11 protocol. The 802.11e medium access control (MAC) protocol is generally recommended for efficient quality of service in WLANs. There are many parameters in the MAC protocol that affect quality of services. Among these parameters, request to send threshold value (RSTV), fragmentation threshold value (FTV) and buffer size (BS) directly affect network performance. RSTV is used in the request to send/clear to send (RTS/CTS) mechanism in the carrier sense multiple access with collision avoidance (CSMA/CA) protocol for collision prevention. This parameter specifies the threshold used to activate the CSMA/CA protocol. FTV is another parameter that is used to send large-sized packets by dividing them into appropriate fragments during CSMA/CA transmission and reduces packet loss in WLAN. BS is another parameter that has a significant cost in the CSMA/CA model and also directly affects the performance. In this article, to improve the performance of WLANs, OPNET Modeler was used and ideal values were obtained for RSTV, FTV and BS by using fuzzy logic-based method. The values obtained by fuzzy logic were re-tested in OPNET Modeler, and the achieved improvement was as follows: for delay 36–38%, for load 2–10% and for throughput 25–44%, respectively. Thus, in WLANs, performance was improved by using fuzzy logic-based method.

     

A study of the length effect of fiber delay line based on CSMA/CP optical packet switching

This paper proposes a novel MAC (media access control) protocol named CSMA/CP for a metropolitan area network for the next generation Internet, which is an OPS (optical packet switch) network that all-optically and directly transfers IP packets over a WDM (wavelength division multiplexing) ring network. The proposed protocol uses the concepts of CSMA (carrier sense multiple access) and CP (carrier preemption) to all-optically transfer the IP packets of the nodes in the WDM ring networks. This paper studies the length effect of FDL (fiber delay line) in each node to support variable packet transmission, and develops an analytical model to analyze and simulate the packet delay and throughput.     

基于IEEE 802.11b无线网络的MAC协议改良冲突解决算法

研究基于介质访问控制协议(MAC)的分布式争用问题的主要焦点就是设计有效的具有高吞吐量性能的MAC协议。该文提出在无线局域网中基于MAC协议的有效争用方法,即改良的冲突解决算法(DCR)。该算法主要做了以下几方面的改良和创新:对所有现用网点主动的分配补偿时间,提高解决冲突的速度;当确定固定数量的连续空闲时间片被探测到时,对成功包传输的站点使用较小的争用窗口,以指数级速度减少补偿时间片和减少空闲时间片的平均数。该文提出的改良冲突解决算法提供了高吞吐量性能和在局域网中的低执行时间。