WLAN上的多媒体业务质量研究

随着无线网络的迅速发展，网络上的业务流量与日俱增，如何保证无线局城网实时业务服务质量的问题也越来越突出．文中分别介绍了IEEE802．11中的MAC层协议和802．11e标准中所采纳的改进方式，通过对比分析DCF和EDCF的性能特性，具体仿真时延和丢包率两个性能参数，指出了802．11e标准对MAC层所做的改进．     

IEEE802．11无线局域网络性能分析

无线局域网是目前无线通信领域中的主要通信网络之一，如何有效的分析IEE802．11无线局域网中的饱和吞吐率和接入时延一直是无线局域网中的研究重点．本文引入了一种新型的分析模型，分析了IEEE802．11DCF协议下Ad Hoc网络的饱和吞吐量，该模型不仅简单而且准确，有效地降低了分析方法的复杂度；同时本文还建立了一种有效的模型，分析了IEEE802．11DCF协议下Ad Hoc网络的接入时延．仿真结果表明所有的分析结果和仿真结果都很吻合，这说明了我们的分析模型是可行的．     

基于TDMA支持实时应用的多跳时隙预留协议

提出一种基于时分多址接入(TDMA)的多跳时隙预留的协议(TMSR)以支持Ad Hoc网络中的实时应用,协议中节点为实时数据包的多跳转发预留信道时隙,通过超帧把数据包从源节点传输到远端的目的节点。通过NS2对提出的协议性能进行评估,重点分析了静态和移动环境下该协议的平均端到端时延和平均吞吐量,同时,在单跳仿真场景中,对TMSR协议与ETDMA进行对比,仿真结果表明随着数据流量的增加,TMSR提供了比E-TDMA更好的数据包吞吐量和时延性能。在多跳仿真场景中,采用TMSR协议的节点间的平均端到端的时延满足了实时应用的端到端多跳时延要求。     

一种贪婪地理路由协议的改进算法

贪婪转发策略广泛应用于无线传感网络(WSNs)的地理路由协议中,但是,该协议存在数据包丢失严重以及在遭遇路由空洞时路由效率低下的不足。为此,提出一种贪婪地理路由协议的改进算法,记为GPSR-I算法。GPSR-I算法在选择下一跳转发节点时,利用节点离目的节点距离、方向以及节点密度信息计算度量值,然后依据该度量值决策下一跳转发节点。仿真数据表明,与GPSR相比,GPSR-I算法能够有效降低平均端到端传输时延、路由开销,并提高了数据包传输率。     

为实时业务提供QoS保证的MAC机制性能研究

分析的MAC机制在IEEE802．11DCF机制的基础上提供了QoS增强。由于实时业务对时延要求敏感。因而提出的实时业务分析模型并未考虑退避重传。和尽力而为业务相比较。实时业务获得了高的饱和吞吐量和低的接入延时，但是以较高的帧丢失率为代价。为了保证实时业务的QoS要求，使用QoS参数P0．Qos来限制帧丢失率。经过分析得出，在保证帧丢失率上限和最大吞吐量的条件下，可求得最优初始窗口，获得较好的网络性能。     

一种基于转发区域的三维地理位置路由协议

在真实的无线传感网络(WSNs)应用环境中,传感节点位于三维空间。为此,提出基于锥形转发区域的三维地理位置路由协议。为了减少冗余数据包数、降低数据包碰撞概率,CFRG协议先建立锥形转发区域,其目的在于限制转发节点数。然后,再估计锥形转发区域内节点的转发概率,最终选择具有最大转发概率的节点转发数据包。当节点遭遇空洞节点问题,就自适应地调整锥形转发区域体积,扩大选择转发节点的空间,即通过锥形转发区域调整,解决VNP问题。仿真结果表明,提出的CFRG协议能够处理VNP问题。与同类的三维路由协议相比,CFRG协议能够提升端到端传输时延和数据包丢失率两方面性能。     

两种MAC层协议对提高无线自组网QoS的分析比较

介绍了无线自组网络中的分布式资源分配协议和IEEE 802．11e协议，并对两种协议在提高网络的吞吐量和端到端的时延性能等方面做了分析比较，仿真结果表明在轻负载情况下，由于802．11e没有采用节点之间的握手联络信号，具有较低的时延；但由于竞争接入信道时缺乏协调控制，丢包率较高。在重负载情况下，分布式资源分配协议的性能指标均优于802．11e。     

Internet服务质量技术综述

Ｉｎｔｅｒｎｅｔ服务质量方面的技术包括集成服务、区分服务、多协议标记交换、业务工程等。集成服务模型的特点是资源预留;区分服务模型是在网络入口路由器处对数据包进行分类和标记,不同类的数据包得到不同的服务;多协议标记交换是在交换域入口处给数据分配一个标记,据此进行分类、转发和服务的转发机制;约束路由是寻找路由的过程受带宽、时延等约束的高级路由机制;业务工程在一开始就考虑网络性能的优化和网络资源的使用以     

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％。     

对WLAN无线网络规划及优化技术的分析

经过理论分析和OPNET仿真比较所提出的针对WLAN无线接入网络的规划从传播预测及覆盖设计方面研究覆盖规划、分析研究基于DCF协议的容量规划以及干扰分析和信道优化配置等方法,能有效的降低数据包的碰撞概率,从而降低了时延,增加了系统吞吐率、和网络容量.提出的基于RTS/CTS机制改进的退避算法是对基于CSMA/CA协议的DCF性能的分析和改进,并得出的饱和条件下系统归一化吞吐率、丢包率、网络延时等性能,以此指标用来指导实际吞吐量的估算和网络容量规划.     

A Delay-Tolerant Virtual Tunnel Scheme for Asynchronous MAC protocols in WSN

Typically, asynchronous MAC protocols are used to monitor a significant facility for rare events or to detect an intrusion in wireless sensor networks. Moreover, asynchronous MAC protocols can achieve high energy efficiency due to the fact that there is no periodic control frame. However, asynchronous MAC protocols have the problem of long end-to-end delay time caused by the absence of precedent time synchronization per link. This paper proposes a new scheme, called virtual tunnel (VT), which can reduce the delivery delay of asynchronous MAC protocols in multi-hop environment. The VT scheme can achieve approximated duty cycle synchronization with on-demand approach. In this scheme, through the estimation of next wakeup time of peer node, without exceptional process, each node on the transmission path can improve end-to-end delay in multi-hop topologies. And it becomes low power consumption by reducing unnecessary retransmissions. Additionally, we devise the protection method of VT. In our simulation results, end-to-end delay according to hop counts and traffic amount is compared with the X-MAC that is an asynchronous protocol recently developed. Furthermore, it is shown that the VT scheme decreases energy consumption due to the lower end-to-end delay than the X-MAC in multi-hop topologies.     

RP-MAC: A Passive MAC Protocol with Frame Reordering for Wireless Sensor Networks

Idle listening is one of the main factors for energy consumption in wireless sensor networks, and the duty cycle mechanism is widely used to reduce idle listening. In this paper, we present a new receiver-initiated duty cycling MAC protocol for wireless sensor networks, called reordering-passive MAC (RP-MAC), which includes receiver wake-up time estimation scheme and frame reordering scheme. We evaluate the performance of RP-MAC in ns-2 network simulator, and the simulation results shows that RP-MAC achieves higher energy efficiency, higher network throughput and lower end-to-end delay compared to other passive protocols, especially in case of heavy traffic or low duty cycle.     

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.     

Distributed Flow Admission Control for Multimedia Services Over Wireless Ad Hoc Networks

In this paper we propose a novel Priority-based Distributed flow Admission Control (PDAC) protocol to provide Quality of Service (QoS) to multimedia applications over the Dynamic Source Routing (DSR) protocol-based wireless ad hoc networks. In contrast to short-term packet forwarding, medium and long-term multimedia and real-time traffic may benefit from ‘flow’-based transmission due to the reduction in the packet-level control overhead. In this paper, we introduce a new DSR option called the “Admission Control Option” for flow establishment, and present a new scalable transmission rate reservation protocol to support bandwidth-constrained traffic flows in interference-limited wireless ad hoc networks. It allows a node in the wireless ad hoc network to establish or discard a traffic flow state based on the global knowledge of traffic flow priority, and local knowledge in the form of interference and effective transmission rate. The PDAC scheme can also operate in a ‘cross-layer’ protocol architecture that encompasses the network layer and the MAC layer.     

An Energy-Efficient Self-Adaptive Duty Cycle MAC Protocol for Traffic-Dynamic Wireless Sensor Networks

A plenty of Medium Access Control (MAC) protocols deal with static traffics with low traffic load. The performance of these protocols drops significantly when network traffic become dynamic or in high traffic load. In this paper, we propose a new MAC protocol called Self-Adaptive Duty Cycle MAC (SEA-MAC) by introducing dual adaptive mechanisms: (1) An Adaptive Scheduling (AS) mechanism which makes the nodes’ active duration adaptive to variable traffic load, thus enabling SEA-MAC to resiliently schedule data transmission for the Sleep period. The algorithm is designated to schedule more data transmission in bursty and high traffic load, thus enabling rapid dissemination of data and reduction of latency. While under the light traffic load, nodes enter the Sleep mode timely, mitigating idle listening and saving energy. (2) A Self-Adaptive duty cycle mechanism which further adjusts the duty cycle and makes SEA-MAC adaptive to the dynamic traffic loads. When network experience with very low or very high traffic load, the protocol further adjusts duty cycle dynamically based on the traffic load, thus reducing inefficient duty cycle or reduce end-to-end delay. Experiment results show that the SEA-MAC is a great advancement compared with AS-MAC and RI-MAC protocols on the performance for unicast scenarios, especially under heavy unicast traffic load. SEA-MAC can reduce average and max end-to-end delay up to 50.90 and 68.20% respectively, lower energy consumption up to about 16.28%, and increase PDR up to about 16% compared with AS-MAC. SEA-MAC superiors to RI-MAC in average end-to-end delay by up to 80% and in maximum end-to-end delay up to 90% for all the traffic load in question. SEA-MAC outperforms RI-MAC significantly in average duty cycle under medium and heavy traffic load.     

Self-adaptive transmission scheme of integrated services over an IEEE 802.11 WLAN

A novel self-adaptive transmission scheme to support integrated data and voice transmission over an IEEE 802.11 WLAN is proposed. The simulation results show that the scheme can improve the data traffic performance and decrease efficiently the voice traffic delay jitter, and then increase the WLAN capacity. It is easy to realise as no change in the MAC protocol is required.     

A forwarding scheme based on swarm intelligence and percolation centrality in opportunistic networks

Incorporating social relationship properties into forwarding schemes in opportunistic networks has become a more and more important paradigm. Communication among the nodes in an opportunistic network relies on intermittent contacts without complete end-to-end paths. Most of these forwarding schemes take advantage of social information such as contact information and social relationship among the nodes in the network. In this paper, we propose a social information based forwarding scheme in opportunistic networks through mimicking honey bees’ behaviors in an artificial bee colony. In the proposed scheme, we adopt the percolation centrality in the social networks to assign certain nodes as “influential” bees. The proposed forwarding scheme is aim at balancing the level between network traffic and transmission delay using the home-cell community-based mobility model (HCMM). Experiments were performed on the network simulator NS-2. The results show that the proposed scheme has outstanding performance for the level of network traffic and transmission delay in comparison to other schemes such as Epidemic, PRoPHET and SimBet when using the HCMM.     

一种基于IEEE802.11支持QoS自适应调度器模型和算法

这篇文章提出了能够有效支持QoS的IEEE802．11自适应调度器模型。和以往的支持QoS的调度器模型相比，这里根据在主控接入点(MAP：Master Access Point)和用户终端(UT：User Termination)的各自延时需求对满足不同的传输机制的分组流进行自适应调度。这种机制不仅完全兼容当前支持QoS的IEEE802．11MAC协议标准，而且能够有效减少由于实时传输带来的分组延时，增加满足不同信道负载和带宽要求的数据流的吞吐率。实时测试得到的数据基本验证了这个要求。     

A Priority Based Opportunistic Routing Mechanism for Real-Time Voice Service in Mobile Ad hoc Networks

Traditional routing protocols send traffic along pre-determined paths and have been shown ineffective in coping with unreliable and unpredictable wireless medium which is caused by the multi-path fading. The most difference between the opportunistic routing and the traditional routing mechanism is that the opportunistic routing mechanism can use several lossy broadcast links to support reliable transmission. In this paper, an opportunistic routing mechanism for real-time voice service is proposed. This mechanism is based on the dynamic source routing (DSR) protocol with some modifications, the routing messages of DSR are used to construct the forwarder list, which guides the data packets forwarding process. The forwarder nodes have priorities to restrict the number of duplicated packets. Simultaneous flows can be supported well by our mechanism. Simulations show that our mechanism can effectively decrease the data packets transmission times and the amount of the control messages and reduce the end-to-end delay for real-time voice service, the quality of service can be supported well over the unstable wireless channel.     

A novel medium access control protocol for passive optical network supporting local area networking capabilities

An alternate solution for Ethernet passive optical networks (EPON) providing local area networking (LAN) capabilities is proposed in this article. Our solution adopts a star coupler-based PON architecture and uses radio frequency subcarrier multiplexed transmission for the LAN traffic delivery. The proposed medium access control (MAC) protocol supports a fully distributed control plane among the optical network units (ONUs) for ONU–ONU communication as well as upstream access to the OLT. The simulation results indicate that the proposed MAC protocol outperforms the others in terms of the average packet end-to-end delay, especially for LAN traffic.