无线Ad hoc网络速率自适应MAC协议研究

无线Ad hoc网络多采用IEEE802.11系列标准,在物理层为数据传输提供了多速率能力。为了充分利用多速率能力提高系统的吞吐量,速率自适应MAC协议根据对当前信道质量的估计,选择最佳的数据传输速率。在分析了速率自适应MAC协议的基本工作过程之后,重点综述了目前存在的速率自适应MAC协议,并讨论了进一步研究的方向。     

无线Ad Hoc网络MAC层速率自适应技术研究

目前的IEEE802.11标准虽然在物理层提供了对多速率的支持,但是在MAC（媒体接入控制,Media Access Control）层却没有规定速率自适应的方法。研究了无线Ad Hoc网络（自组织网）中的速率自适应技术,针对RBAR协议存在的不足提出了一种改进的MAC层速率自适应协议,该协议实现简单,与标准的兼容性好,对信道的变化适应能力更强。仿真结果表明,该协议比RBAR协议具有更好的性能。     

Ad hoc网络的体系结构及其设计

Adhoe网络体系结构的设计问题目前仍无定论，但是有一点是可以确定的，即应采用不同于传统网络的体系结构。首先阐述Ad：hoe网络的节点结构，比较了几种典型的网络结构，然后给出了一种用于Adhoe网络的通用协议栈。接着详细地讨论了Ad：hoe网络体系结构的设计策略、原则和方法，最后对全文进行了小结并给出了今后的工作方向。     

无线Ad hoc网络及其路由协议

介绍了无线Ad hoc网络的发展和特点,并对当前提出的重要的路由协议进行了总结归纳。     

Ad hoc网络的体系结构及其设计

Ad hoc网络体系结构的设计问题目前仍无定论,但是有一点是可以确定的,即应采用不同于传统网络的体系结构。首先阐述Ad hoc网络的节点结构,比较了几种典型的网络结构,然后给出了一种用于Ad hoc网络的通用协议栈。接着详细地讨论了Ad hoc网络体系结构的设计策略、原则和方法,最后对全文进行了小结并给出了今后的工作方向。     

基于IEEE 802.11高速无线局域网的速率自适应MAC协议研究

目前的IEEE 802.11标准在物理层提供了对多种发送速率的支持,然而在MAC层却没有规定速率自适应的方法。该文研究了高速IEEE 802.11 无线局域网中的速率自适应方案。首先,提出了EACK协议,EACK使用基本速率发送MAC头,并在ACK帧中携带信道信息,因而能够较快速地响应信道的变化,同时具有少的开销;其次,在EACK基础上,提出了一种恒定发送时间(CEACK)的策略,CEACK能够克服传统IEEE 802.11 DCF MAC协议的理论吞吐量上限,并且具有更好的时间公平性能,能够应用于高速的无线局域网。     

认知无线Ad hoc网络的认知体系结构研究

对认知无线Ad hoc网络进行了阐述。对于认知无线Ad hoc网络,要考虑到无线Ad hoc网络的整体特点,来研究网络级认知结构。而由于认知无线Ad hoc网络是基于无线Ad hoc网络体系结构,同时鉴于无线Ad hoc网络本身特点,因此网络体系参数和网络本身特性参数共同被定义为认知信息,并在与跨层设计结合基础上进行节点级认知结构设计。认知信息的获取与传输方式将认知无线Ad hoc网络网络级与节点级结构有机地联合起来,使整个认知体系成为完整有机体。     

Ad hoc网络跨层设计研究

由于无线链路和拓扑结构的时变特性,隐终端和暴露终端问题,Ad hoc网络的优化设计是一个很复杂的问题,跨层设计的提出就是为了解决这个难题。文章介绍Ad hoc网络跨层设计的提出背景,理论依据以及跨层设计的原则和目标,提出一种较合理的跨层设计模型,分析了跨层设计中存在的关键问题。     

一种基于IEEE 802.11的多速率自适应MAC协议

提出了一种新颖的基于连续ACK帧统计信息的IEEE 802.11多速率自适应MAC协议EARF(EnhancedARF),其主要思想是:每一个速率有各自的成功阈值——速率升高的门限值,并且该值根据信道状况(用延时因子量化)动态地变化。协议不需对现有的IEEE 802.11标准做任何修改,因此易于通过编写驱动程序实现。仿真表明在大多数信道条件下,该协议性能较现有的基于ACK帧统计的速率自适应协议如ARF,ARF3-10都有较大的提高。     

Ad hoc网络中MAC协议的研究

Adhoc网络中的MAC协议是一个比较复杂的问题。本文首先分析了Adhoc网络中实施MAC协议的各种困难,然后详细讨论了隐终端和暴露终端问题。最后比较分析了目前提出的几种Adhoc环境下的MAC协议并给出了结论。     

一种自组网功率控制算法及分析

无线自组网中的移动节点大多依靠电池提供能量,因此能量是影响无线自组网性能的一个很大的瓶颈,作为事实上的无线自组网媒体接入协议,802.11并没有动态调整传输功率的能力,大大限制了网络的生存时间。采用功率控制可以提高节点的功率使用效率,减少相邻节点间的干扰,改善网络的性能。在802.11基础上提出一种基于信噪比的动态传输功率控制算法。通过进行计算机仿真,与802.11协议相比,在保持吞吐量性能的前提下,大大减少了节点的功率消耗,提高了节点的能量利用率。     

A High-Throughput MAC Protocol for Wireless Ad Hoc Networks

One way to improve the throughput of a wireless ad hoc network at the media access (MAC) layer is to allow as much as possible concurrent transmissions among neighboring nodes. In this paper, we present a novel high-throughput MAC protocol, called Concurrent Transmission MAC(CTMAC), which supports concurrent transmission while allowing the network to have a simple design with a single channel, single transceiver, and single transmission power architecture. CTMAC inserts additional control gap between the transmission of control packets (RTS/CTS) and data packets (DATA/ACK), which allows a series of RTS/CTS exchanges to take place between the nodes in the vicinity of the transmitting or receiving node to schedule possible multiple, concurrent data transmissions. To safeguard the concurrent data transmission, collision avoidance information is included in the control packets and used by the neighboring nodes to determine whether they should begin their transmissions. Also, to isolate the possible interference between DATA packets and ACK packets, a new ACK sequence mechanism is proposed. Simulation results show that a significant gain in throughput can be obtained by the CTMAC protocol compared with the existing work including the IEEE 802.11 MAC protocol.     

Energy-efficient Rate Adaptation MAC Protocol for Ad Hoc Wireless Networks

In this paper, two novel energy-efficient rate adaptation schemes are presented. The proposed protocols use the Distributed Power Control (DPC) algorithm to predict the channel state and determine the necessary transmission power which optimizes the energy consumption. The first proposed rate adaptation scheme heuristically alters the modulation rate to balance the energy-efficiency and the required throughput which is estimated with queue fill ratio. Moreover, the back-off scheme is incorporated to mitigate congestion and reduce packet losses due to buffer overflows thus minimizing energy consumption. Consequently, the nodes will conserve energy when the traffic is low, offer higher throughput when needed and save energy during congestion by limiting transmission rates. The second rate adaptation scheme employs dynamic programming (DP) principle to analytically select modulation rate and a burst size to be used during transmission. The proposed quadratic cost-function minimizes the energy consumption while alleviating network congestions and buffer overflows. The proposed DP solution renders a Riccati equation ultimately providing an optimal rate selection. The simulation results indicate that an increase in throughput by 96% and energy-efficiency by 131% is observed when compared to other available protocols, for example Receiver Based AutoRate (RBAR).

A Hybrid Token-CDMA MAC Protocol for Wireless Ad Hoc Networks

Token-passing medium access control (MAC) protocols are gaining interest among wireless ad hoc network researchers as they provide unrivaled advantages over the existing IEEE 802.11 standards. This paper introduces a hybrid token-code division multiple access (CDMA) MAC protocol that is based on a token-passing scheme with the incorporation of CDMA. With its unique CDMA feature, the proposed MAC is able to support multiple simultaneous transmissions. The proposed protocol provides both quality of service (QoS) and high network resource utilization while ensuring the stability of the network. This paper examines the performance of the proposed MAC scheme by simulation and compares its performance against that of other MAC protocols that have appeared in the literature. Simulation results demonstrate that our proposed MAC scheme is effective in decreasing the packet delay and significantly shortens the length of the queue. The input traffic model used in the simulation is a two-state Markov-Modulated Poisson Process (MMPP). The data rate QoS is enforced by implementing a modified leaky bucket mechanism in the proposed MAC scheme. The simulation also takes into account channel link errors caused by the wireless link by implementing a multilayered Gilbert-Elliot model.     

基于位置信息的大区域移动自组网MAC协议

针对大区域移动自组网提出一种基于位置信息的MAC协议(PB-MAC).该协议采用CSMMCA方式来交换控制信息,采用TDMA方式进行数据业务传输,并在位置信息的辅助下对数据传输进行时隙调整.仿真结果表明,PB-MAC能有效提高网络吞吐量,提供确定的延时上界,并使网络保持较好的可扩展性.     

基于负载均衡的Ad Hoc网络多信道MAC协议

在Ad hoc网络多信道MAC层协议中,信道的负载均衡问题会影响系统的性能,已有的负载均衡方法大多基于载波侦听技术,给每个数据信道配置一个物理载波侦听模块,这增加了设备复杂度和系统能耗。为此,提出了一种新的基于虚拟载波侦听的负载均衡方法,系统设置负载信息表记录每个数据信道的负载信息,使节点不需要侦听模块就可以获取数据信道上的负载量。仿真结果表明该方法提高了系统的性能。     

基于干扰图的无线自组织网络MAC协议

由于IEEE802．11MAC协议采用了简单的干扰模型，因此产生了隐藏终端和暴露终端这两个严重影响无线自组织网络性能的问题。文章提出了一种新的基于干扰图（Conflict Graph）的MAC协议——CG-MAC来提高无线自组织网络的吞吐量。通过仿真实验，该协议能够同时解决隐藏终端和暴露终端问题．很大程度地提高了网络性能。     

一种自适应侦听的异步无线传感器网络MAC协议

为了提升异步无线传感器网络MAC协议在动态网络负载下的性能,论文提出了一种流量自适应的异步协议AA-MAC.该协议基于短前导序列采样技术,当节点收稿数据后并不理解转入睡眠而自适应增加若干个最短侦听时间用以接收发送节点的可能其他数据,使得收发双方在网络负载较重时能实现一次配对多次收发数据.分析并对比了AA-MAC和X-M...     

Congestion Aware Geographic Routing Protocol for Wireless Ad Hoc and Sensor Networks

Geographic routing protocols forward packets according to the geographical locations of nodes. Thus, the criteria used to select a forwarding node impacts on the performance of the protocols such as energy efficiency and end-to-end transmission delay. In this paper, we propose a congestion aware forwarder selection (CAFS) method for a geographic routing protocol. To design CAFS, we devise a cost function by combining not only the forward progress made to a packet but also the amount of energy required for packet forwarding, forwarding direction, and congestion levels of potential forwarders. Among the potential forwarders, CAFS selects the next forwarder having the minimum cost. In our simulation studies, we compare the performance of CAFS with those of the maximum progress (MP) method and the cost over progress (CoP) method in various network conditions. The results show that compared with MP, the length of a routing path in terms of the number of hops becomes longer when CAFS is used. However, the shorter hop distance helps to avoid unnecessary retransmissions caused by packet loss in a wireless channel. In addition, since CAFS considers congestion levels of candidate forwarders, it reduces the queuing delay in each forwarder. Therefore, CAFS is superior to the MP and the CoP in terms of the energy consumption, end-to-end packet transfer delay, and the successful packet delivery rate.