无线移动网络的协作通信方案研究

结合具体的无线Ad hoc网络,提出了机会性的根据网络实时状况选择最佳中继的协作MAC协议,并在NS-2仿真平台上实现,仿真结果表明,较常规的802.11 DCF协议,协作MAC方案有效地提高了网络的递交率。此外对采用RCPC编码协作的MAC协议进行了数值仿真。这些协议和方案可以直接或修改后应用于现有的Ad hoc等无线网络,在一定程度上可以实现跨层的机会协作通信和组网方案。     

Ad Hoc中一种改进后退机制的基于多包接收的MAC算法

物理层多包接收技术的发展给利用物理层多包接收能力的媒体接入控制（MAC）协议的设计带来了挑战。IEEE802.11 DCF是目前WIAN最成熟的分布式MAC协议之一，对其在多包接收模型下进行性能改善将有很大的应用价值。在物理层具有多包接收能力的基础上，提出了一种改进的802.11 DCF协议，并将该协议应用于现有的基于802.11 DCF的多包接收MAC算法（MDCF），理论分析和NS-2仿真实验结果表明，该算法与IEEE 802.11 DCF和MDCF相比，在网络吞吐量和时延性能方面有很大的改善。     

一种基于全双工的无线网络MAC协议设计与性能分析

半双工无线电台使用两个独立频段实现信息同时发送和接收,而全双工无线电台则使用一个频段实现信息同时收发。为了进一步提升全双工网络性能,提出一种应用于全双工网络的简单高效的MAC协议——全双工MAC（full duplex MAC,FD-MAC）协议,该协议能够兼容IEEE 802.11 MAC协议。在综合考虑物理层和MAC层的基础上,分析了使用FD-MAC协议的全双工无线网络的性能。数值和仿真结果证明,和已有的全双工网络MAC协议相比,FD-MAC协议具有更优的网络吞吐性能和更低的能量消耗。     

一种改善TCP性能的cdma2000链路层RLP重传方案

在无线数据传输网络中,物理层帧差错率(FER)是影响网络性能的一个主要因素。无线链路层重传技术是改善网络性能因无线信道误码率较高而下降的一项重要措施。本文主要研究cdma2000无线网络中链路层重传技术对无线TCP数据传输的影响,提出一种cdma2000链路层重传方案,并通过OPNET仿真技术对该重传方案进行仿真,验证了该方案能改善TCP数据在cdma2000无线网络中的传输性能。     

802.11WLAN中一种基于循环队列的分布式公平队列调度算法

该文在无线局域网现有的802.11 MAC层访问机制的基础上,运用循环队列的思想提出了一种完全分布式的队列调度算法,该算法通过修改802.11的MAC层中的DCF(Distributed Coordination Function)子协议,实现了在分布式环境下控制802.11节点的公平访问无线链路资源的目的。文中通过仿真对算法进行了分析和研究,仿真结果表明该方法可以在一定范围内实现公平队列调度。     

多层建筑室内无线网络的协作安全研究

多层建筑室内无线网络安全问题的特殊性,主要由其具有随机性、动态性和复杂性的空间拓扑结构所引起的。针对多层室内无线网络节点分布随机、空间结构复杂、损耗类型多样等特点,该文结合物理层安全与随机几何理论,对多层室内无线网络中的多节点协作安全传输展开研究。首先,基于多层泊松点过程对K层室内无线网络进行建模;在此基础上,将协作传输引入多层室内无线网络,并提出该网络的安全概率分析框架;随后,结合理论推导及仿真,分析了楼层总数、安全速率门限、用户所处楼层和各层发射功率配置等因素对多层室内无线网络安全性能的影响。最后,通过仿真验证了协作传输能够有效提高室内无线网络的安全性能。     

基于太赫兹无线网络的高速MAC协议研究与实现

为解决现有无线网络的MAC协议无法匹配太赫兹无线网络物理层(PHY)的问题,提出了一种新的太赫兹无线网络MAC协议,并对该协议加以实现验证。该协议通过新的超帧结构,减少了数据发送的等待时间,加快了端到端数据的传输,从而获得更高的网络端到端吞吐量。通过实现结果表明,在带宽为3.125 Gbps下,采用新协议可以实现均值约2.78 Gbps的端到端吞吐量;同时,在端到端平均时延的性能上也有较大提升。该协议的实现为将来太赫兹无线网络MAC协议的进一步研究提供了有力的支持。     

基于NS2的IEEE802.11MAC仿真模块分析

在对IEE802.11MAC的分布式协调功能DCF和NS2仿真软件进行简单介绍的基础上,深入分析了NS2中IEEE802.11MAC仿真模块的系统结构和协议仿真流程实现细节,并进行了简单的仿真实验与性能分析.为NS2下进行无线网络仿真与协议代码的扩展提供了参考.     

X-MAC:一种新型的无线传感器网络MAC协议﹡

在无线传感器网络体系结构中,MAC(Medium Access Control)协议是保证网络高效通信的重要协议.无线传感器网络有着与传统无线网络明显不同的性能特点和技术要求.对于很多的 MAC 层协议而言,吞吐量很大程度上受到了物理信道的利用率和协议开销的限制.这里设计了一种基于一对多拓扑的无线传感器Mac层网络协议.最后,还通过NS-2(Network Simulator 2)仿真并比较该协议与现存无线传感器MAC层网络协议的网络性能.     

一种用于AdHoc网络的协同MAC协议

基于IEEE802．11 DCF模型,利用协同分集技术,提出了一种适用于AdHoc网络的协同MAC协议。此协议在目的节点实时选择传输模式和协同节点,可有效减小节点移动和信道变化对网络性能产生的影响。同时,利用分集技术,对源节点和协同节点的数据信号进行最大比合并（MRC）,可有效提高系统的可靠性。仿真结果表明,在文中的仿真条件下,和传统IEEE802．11DCF协议相比,该协议在系统分组递交率和延迟性能上分别提高了20％和50％。     

Performance Analysis of IEEE 802.11 DCF in Imperfect Channels

IEEE 802.11 is the most important standard for wireless local area networks (WLANs). In IEEE 802.11, the fundamental medium access control (MAC) scheme is the distributed coordination function (DCF). To understand the performance of WLANs, it is important to analyze IEEE 802.11 DCF. Recently, several analytical models have been proposed to evaluate the performance of DCF under different incoming traffic conditions. However, to the best of the authors' knowledge, there is no accurate model that takes into account both the incoming traffic loads and the effect of imperfect wireless channels, in which unsuccessful packet delivery may occur due to bit transmission errors. In this paper, the authors address this issue and provide an analytical model to evaluate the performance of DCF in imperfect wireless channels. The authors consider the impact of different factors together, including the binary exponential backoff mechanism in DCF, various incoming traffic loads, distribution of incoming packet size, queueing system at the MAC layer, and the imperfect wireless channels, which has never been done before. Extensive simulation and analysis results show that the proposed analytical model can accurately predict the delay and throughput performance of IEEE 802.11 DCF under different channel and traffic conditions.     

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。     

Throughput behavior of link adaptive 802.11 DCF with MUD capable access node

Conventional IEEE 802.11 medium access control (MAC) protocol discourages simultaneous transmission to avoid collisions. With fast advances in physical layer technologies, multi-user detection (MUD) capable receivers which can detect multiple frames from different users simultaneously become available. If we are to utilize them in today's wireless LAN, however, it is not entirely clear how we should change the MAC and how much benefit is available and can be obtained by doing so. The primary objective of this paper is to investigate such questions. We approach this objective by developing a new throughput expression for 802.11 distributed coordination function (DCF). The derived expression has been verified in simulation. We show that significant throughput gain can be garnered with slight modification in 802.11 DCF.     

IEEE802.11s路由协议漏洞与攻击

IEEE802.11s是IEEE关于无线Mesh网络的规范。802.11s虽然沿用了IEEE802.11i的安全规范,但是对于路由协议的安全并没有做过多的定义,由此产生了一定的安全隐患。文章分析了IEEE802.11s标准(草案)中的路由协议的漏洞,并针对IEEE802.11s中使用的混合无线网状网协议(HybridWirelessMeshProtocol,HWMP)设计了两种攻击方式,从而破坏无线网状网络的可用性。通过在自行设计的路由器平台上实现无线攻击,并分析攻击对网络造成的影响来验证安全漏洞的存在性和可利用性。     

IEEE 802．11网络分析模型

IEEE 802.11在MAC层采用DCF作为主要的信道接入方式。本文分析了现有的几种802.11网络分析模型,其中B ianch i模型很好的描述了饱和状态下802.11 DCF的性能;X iao模型针对802.11e进行了多优先级的扩展,实现了EDCF的性能分析。最后介绍了一种新的分析模型,新模型同时考虑了业务优先级和内部调度算法,够较准确地描述网络性能。     

A novel self‐adaptive transmission scheme over an IEEE 802.11 WLAN for supporting multi‐service

The IEEE 802.11 wireless local area network (WLAN) media access control (MAC) specification is a hybrid protocol of random access and polling when both distributed coordination function (DCF) and point coordination function (PCF) are used. Data traffic is transmitted with the DCF, while voice transmission is carried out with the PCF. Based on the performance analysis of the MAC protocol for integrated data and voice transmission by simulation, this paper puts forward a self‐adaptive transmission scheme to support multi‐service over the IEEE 802.11 WLAN. The simulation results show that, on the premise of satisfying the maximum allowable delay of packet voice, the self‐adaptive transmission scheme can improve the data traffic performance and increase the WLAN capacity through dynamic and appropriate adjustment of the protocol parameters. Especially, voice traffic is sensitive to delay jitter, and the self‐adaptive scheme can effectively decrease it. Finally, it is worth noting that the adaptive scheme is easy to be realized, whereas no change in the MAC protocol is needed. Copyright © 2006 John Wiley & Sons, Ltd.     

IEEE 802.11s网络及其性能评估

无线局域网标准IEEE 802.11是一种较低成本的无线数据传输方案。无线网状网的产生解决了无线局域网覆盖范围小的问题。IEEE Task Group S早在2004年就开始策划制定关于无线网状网多跳通信,MAC层路由转发以及安全的标准——IEEE 802.11s。介绍了IEEE 802.11s最新的草案标准,并通过试验床的设计与试验评估了当前基于IEEE 802.11s无线网状网网络的整体性能。最后探讨了视频应用在IEEE 802.11s中的可行性。     

SoftMAC: Layer 2.5 Collaborative MAC for Multimedia Support in Multihop Wireless Networks

In this paper, we present the challenges in supporting multimedia, in particular, VoIP services over multihop wireless networks using commercial IEEE 802.11 MAC DCF hardware, and propose a novel software solution, called Layer 2.5 SoftMAC. Our proposed SoftMAC resides between the IEEE 802.11 MAC layer and the IP layer to coordinate the real-time (RT) multimedia and best-effort (BE) data packet transmission among neighboring nodes in a multihop wireless network. To effectively ensure acceptable VoIP services, channel busy time and collision rate need to be well controlled below appropriate levels. Targeted at this, our SoftMAC architecture employs three key mechanisms: 1) distributed admission control for regulating the load of RT traffic, 2) rate control for minimizing the impact of BT traffic on RT one, and 3) nonpreemptive priority queuing for providing high priority service to VoIP traffic. To evaluate the efficacy of these mechanisms, extensive simulations are conducted using the network simulator NS2. We also implement our proposed SoftMAC as a Windows network driver interlace specification (NDIS) driver and build a multihop wireless network testbed with 32 wireless nodes equipped with IEEE 802.11 a/b/g combo cards. Our evaluation and testing results demonstrate the effectiveness of our proposed software solution. Our proposed collaborative SoftMAC framework can also provide good support for A/V streaming in home networks where the network consists of hybrid WLAN (wireless LAN) and Ethernet     

Improving protocol capacity for UDP/TCP traffic with model-based frame scheduling in IEEE 802.11-operated WLANs

In this paper, we develop a model-based frame scheduling scheme, called MFS, to enhance the capacity of IEEE 802.11-operated wireless local area networks (WLANs) for both transmission control protocol (TCP) and user datagram protocol (UDP) traffic. In MFS each node estimates the current network status by keeping track of the number of collisions it encounters between its two consecutive successful frame transmissions, and computes accordingly the current network utilization. The result is then used to determine a scheduling delay to be introduced before a node attempts to transmit its pending frame. MFS does not require any change in IEEE 802.11, but instead lays a thin layer between the LL and medium access control (MAC) layers. In order to accurately calculate the current utilization in WLANs, we develop an analytical model that characterizes data transmission activities in IEEE 802.11-operated WLANs with/without the request to send/clear to send (RTS/CTS) mechanism, and validate the model with ns-2 simulation. All the control overhead incurred in the physical and MAC layers, as well as system parameters specified in IEEE 802.11, are figured in. We conduct a comprehensive simulation study to evaluate MFS in perspective of the number of collisions, achievable throughput, intertransmission delay, and fairness in the cases of TCP and UDP traffic. The simulation results indicate that the performance improvement with respect to the protocol capacity in a WLAN of up to 300 nodes is 1) as high as 20% with the RTS/CTS and 70% without the RTS/CTS in the case of UDP traffic and 2) as high as 10% with the RTS/CTS and 40% without the RTS/CTS in the case of TCP traffic. Moreover, the intertransmission delay in MFS is smaller and exhibits less variation than that in IEEE 802.11; the fairness among wireless nodes in MFS is better than, or equal to, that in IEEE 802.11.