基于多门限估计节点个数的自适应退避算法

针对现有接入协议的性能随着WLAN中节点个数增加而显著下降的问题,本文提出一种新的基于多门限估计激活节点个数的自适应退避算法.该算法优化了时延模型,针对最优退避竞争窗口,分析给出了竞争窗口是激活节点数目的线性函数以及准确的窗系数计算方法;通过更公平地计算空闲时隙间隔,使用三个门限来识别节点个数变化的四种情况,实现了节点个数的估计.理论分析表明,该退避算法使得碰撞概率较小并能获得较高的总吞吐量,同时节点个数的变化对性能影响较小.仿真验证了分析的正确性和算法较好的可扩展性,在公平性方面也优于其它算法.     

基于Ad hoc网络的退避算法研究

在移动Ad hoc网络中,无线信道由多个节点共享,合理协调多个节点访问共享信道的媒体接入控制(MAC,Medium Access Control)协议是移动Ad hoc网络的关键技术之一。退避算法在MAC协议中起着至关重要的作用。针对目前退避算法存在的问题,本文提出了一种改进算法,根据网络节点发送数据包成功与否,预测网络信道空闲或繁忙的趋势,应用趋势合理地调节退避算法中节点发送数据时退避值的大小,并通过Omnet++软件对算法进行了仿真分析对比。     

一种新的增加Ad hoc 网络吞吐量的MAC协议设计

该文提出一种新的MAC协议,其目的是增加802.11b的网络容量。虽然IEEE的802.11b协议提供了较高的原始速率,但是物理层和MAC层随速率提高而引入的额外开销也不断增大。此外,物理层规范定义了两种物理层数据单元格式,但是研究者没有研究如何利用开销小的物理层数据单元来提高802.11b的容量。该文提出一种物理层自适应的算法,它能自适应地选择802.11b物理层规范中的两种不同物理层数据单元格式进行传输,并计算相应的网络分配向量。通过NS仿真证明,该协议能够提高网络的性能,如端到端的时延,有效吞吐量和传包率,特别是在高负载,高速率情况下。     

IEEE 802.11 DCF的一种优化退避算法

为了提升无线网络的整体性能,通过IEEE 802.11 MAC(媒体访问控制)层DCF(分布式协调功能)在基本工作模式下所使用的二进制退避算法和CW(竞争窗口)的大小对网络整体性能的影响进行了分析。采用了增大初始 CW、取消信道从忙碌变为空闲后继续退避需要等待的DIFS (分布式帧间间隔)和设置一个中间值作为阀值使得节点发送失败或成功后采用不同的退避算法进行退避这3种措施来优化DCF方式下的退避机制。经 OPNET仿真验证,改进算法能够有效地降低网络接入时延并能提高网络吞吐量。     

ad hoc网络中数据管理与传输算法的研究

数据的管理与有效传输是ad hoc网络资源能否得到最大化利用,实现网络的最优化运行的一个关键因素.本文利用数据管理的方法,实现相关数据的有效传输以及对数据的有效调度,解决了网络资源浪费问题,并减少了单个节点执行多个任务花费的时间.     

基于IEEE 802.11的无线Ad hoc网络的接入性能研究

无线Ad hoc网络对无线接入平台有着独特的要求，当前广泛使用的是基于IEEE802．1l标准的接入平台。本文从理论和仿真两个方面考察IEEE802．1l标准采用的CSMA／CA接入方式对于无线多跳Ad hoc网络接入性能的影响，并找出制约该性能的因素。     

无线网络预约退避算法的实现和分析

针对无线局域网IEEE 802.11MAC层二进制退避算法的不足,当前已经提出多种典型退避算法。主要针对预约发送类退避算法进行研究分析,并提出与EBA不同的实现措施,对NS2网络仿真软件的Mac802.11模块进行了修改和扩展,实现了NS2对改进的预约退避算法的实现。结果表明,与标准DCF相比,改进的预约退避算法也能对IEEE802.11无线局域网的吞吐量、时延等方面性能有所改善。为今后基于NS2对预约退避算法的进一步开发研究奠定基础。     

基于预警优先级的ZigBee传感网络MAC层退避算法

针对无线传感器网络中有预警信息的高优先级数据包需要尽快传输,且IEEE 802.15.4协议本身不支持任何优先级传输机制的情况,提出了一种基于预警优先级的非时隙CSMA/CA自适应调整阶梯退避算法,并建立了离散时间马尔可夫分析模型,比较分析了网络中不同优先级节点的信道接入概率、网络吞吐量和传输延时,仿真结果表明,本文改进的自适应调整阶梯退避机制对提高无线传感器网络中高优先级数据包的实时传输性能具有积极的作用。     

Ad Hoc网络退避算法分析及改进

IEEE 802.11 DCF中采用的标准退避算法是二进制指数(BEB)退避算法,为了提高该算法在网络中的效能,文中主要研究了BEB算法存在的缺陷,和改进后的线性减少(MILD)退避算法存在的优势,基于OPNET网络仿真平台,对两种算法的性能进行了仿真评估。仿真结果表明,改进的MILD算法对提高Ad Hoc网络的吞吐量性能和公平性有明显的效果。     

IEEE 802．11 DCF中带优先级的退避算法

该文针对IEEE 802.11 DCF提出一个带优先级的退避算法.算法的基本思想是网络中的节点在侦听信道的同时,搜集其他节点发送数据的统计信息,并在本地维护一个关于节点已发送数据量的统计表.当节点有数据需要发送时,将根据表中的统计数据以及本节点的优先级来计算竞争窗口.计算机仿真证明,该算法能很好地完成网络的信道容量在不同优先级的节点之间按一定的比例分配,同时还可提高整个网络的吞吐率.     

Adaptive backoff scheme for ad hoc networks based on IEEE 802.11

The performance of backoff scheme plays an important role in designing efficient Medium Access Protocols for ad hoc networks. In this paper, we propose an adaptive backoff scheme and evaluate the performance of the proposed scheme for ad hoc networks. The backoff mechanism devised by us grants a node access to the channel based on its probability of collision for a transmitted frame in comparison to the nodes in the two‐hop contention area. We use both an analytical model and simulation experiments to evaluate the performance of our adaptive backoff mechanism in an ad hoc network. The results show that our protocol exhibits a significant improvement in power saving, end‐to‐end goodput, packet delivery ratio, and hop‐put, compared with the existing IEEE 802.11 DCF. Copyright © 2010 John Wiley & Sons, Ltd.     

一种新的基于多包接收的ad hoc网络媒体接入算法

多包接收技术在无线网络中的应用为提高网络吞吐量提供了一种新思路。本文在结合多包接收技术的基础上提出了一种应用于ad hoc网络的新的媒体接入控制算法，并对其吞吐量作了分析，与IEEE802．11MAC接入方式进行了性能比较。仿真结果表明，在业务量大于某一特定值时，新算法可以显著的提高ad hoc网络的吞吐量。     

一种基于网络拥塞程度阀值的退避算法

对IEEE802.11无线网络MAC层的技术所使用的DCF协议的退避算法进行了分析,针对二进制指数退避算法BEB存在的不足,提出了改进的退避算法。通过OPNET仿真,仿真结果表明,改进的退避算法能提高网络吞吐量,改善网络性能。     

Increasing fairness and efficiency using the MadMac protocol in ad hoc networks

The IEEE 802.11 MAC layer is known for its unfairness behavior in ad hoc networks. Introducing fairness in the 802.11 MAC protocol may lead to a global throughput decrease. It is still a real challenge to design a fair MAC protocol for ad hoc networks that is distributed, topology independent, that relies on no explicit information exchanges and that is efficient, i.e. that achieves a good aggregate throughput. The MadMac protocol deals with fairness and throughput by maximizing aggregate throughput when unfairness is solved. Fairness provided by MadMac is only based on information provided by the 802.11 MAC layer. MadMac has been tested in many configurations that are known to be unfair and compared with three protocols (IEEE 802.11 and two fair MAC protocols). In these configurations, MadMac provides a good aggregate throughput while solving the fairness issues.     

Ad hoc网中基于位置信息的QoS路由算法

在分析ad hoc网络的单播QOS路由问题的基础上，本文提出了一种新的分布式QoS路由算法-LMLAR(local multicasting location-aided routing)算法。LMLAR算法最关键的思想是利用了“本地多播”机制和位置信息选择路由。仿真结果表明：LMLAR算法能够以较小的路由消息开销取得较高的路由成功率，具有比TBP算法更好的性能，适合于adhoc网的高度动态的环境。     

面向无线ad hoc网络的一种平面t-支撑图

拓扑控制算法的目标是为无线ad hoc网络确定合适的底层拓扑。在无线ad hoc网络中，几何路由协议是一类重要的路由协议，为了保证消息转发的可达性和限制路由长度，它要求底层拓扑满足连通性、平面性和稀疏性，并且是原拓扑的t-支撑图。本文提出了一种新的几何结构AUDel图，并提出了两种低通信开销的构造AUDel图的局部拓扑控制算法。理论分析表明，AUDel图满足上述要求，我们提出的拓扑控制算法的通信歼销小于其它构造平面t-支撑图的拓扑控制算法。模拟实验验证了以上结论。     

A distributed Newton algorithm for network utility maximization in wireless ad hoc networks

The existing distributed Newton algorithm for network utility maximization cannot be directly applied into the wireless ad hoc networks, as it does not consider the wireless link capacity variation and transmission power consumption. Regarding these, a new joint network utility maximization problem is formulated to optimize the wireless ad hoc network resource utility. The distributed Newton algorithm is implemented to solve for the dual variables and Newton directions by using the local information at each session source and link, respectively. Furthermore, a new iterative method is proposed to improve the convergence rate of the existing matrix‐splitting method. Simulation results validate the efficiency and efficacy of the proposed distributed Newton algorithm for wireless ad hoc network utility maximization.     

A power efficient solution to the large interference range problem in ad hoc networks

Due to the mismatch between the transmission range and interference‐vulnerable range, the reception at a receiving node in a wireless network could still be interfered by a sending node beyond the coverage of its clear‐to‐send (CTS). This is the so‐called large interference range problem. It is a common problem in real environments but overlooked by the standards and related studies. The large interference range problem could lead to transmission control protocol (TCP) instability and TCP unfairness, especially in case of multi‐hop transmission. There exist research works devoted to this issue. However, more power consumption was incurred at the same time. For a power‐efficient solution to this problem, a novel scheme, named power control interference avoidance (PCIA), is developed and presented in this article. The proposed scheme decouples control channel from data channel and use different power level in the transmission of control frames and data frames. By doing so, the large interference problem can be effectively avoided, while retaining a high level of power efficiency. The feasibility and effectiveness of the proposed scheme had been validated by an analytic study on a simplified model and a series of simulations. As revealed in the simulation results, the proposed PCIA scheme outperforms conservative CTS reply (CCR) and IEEE 802.11 in many aspects, including data corruption ratio and power efficiency. Copyright © 2008 John Wiley & Sons, Ltd.     

移动自组织网络中的多信道 MAC 调度码的设计与分析

基于有限域上多项式,设计了一类用于支持多类业务移动自组织网络的多信道拓扑透明MAC调度码。这类调度码能够为各类节点提供有保证的服务质量,并且能够利用多信道资源有效地减小码长。性能分析表明,这类拓扑透明MAC调度码在码长以及最小保证吞吐量等方面优于扩展的TDMA固定分配方案。     

Optimized priority based energy efficient routing algorithm for mobile ad hoc networks

Recently more and more research interest focuses on the energy efficient routing in mobile ad hoc networks and many related routing algorithms are reported. In this paper, a new optimized priority based energy efficient routing algorithm is presented and priority is added to the existing routing algorithm according to the residual energy proportion of the nodes. Lower residual energy means lower priority and the nodes with lower priority are less likely to forward packets to other nodes. The algorithm needs no global information of the networks and only a little modification is needed to the existing algorithm, so it is practical to be implemented. The algorithm can improve the performance of routing discovery, routing maintenance and cache management at the same time. Some optimization strategy is taken to reduce the network overhead and the lifetime of the network is much longer and the network with our algorithm can transfer much more effective data. Simulation with NS-2 is done and satisfying results are obtained with this algorithm. The results show that the algorithm is efficient.