A simulation study of service differentiation for the bandwidth request scheme in fixed IEEE 802.16 network

Various flexible mechanisms related to quality of service (QoS) provisioning have been specified for uplink traffic at the medium access control (MAC) layer in the IEEE 802.16 standards. Among the mechanisms, contention based bandwidth request scheme can be used to indicate bandwidth demands to the base station for the non-real-time polling and best-effort services. These two services are used for most applications with unknown traffic characteristics. Due to the diverse QoS requirements of those applications, service differentiation (SD) is anticipated over the contention based bandwidth request scheme. In this paper we investigate the SD with the bandwidth request scheme by means of assigning different channel access parameters and bandwidth allocation priorities at different packets arrival probability. The effectiveness of the differentiation schemes is evaluated by simulations. It is observed that the initial backoff window can be efficient in SD, and if combined with the bandwidth allocation priority, the SD performances will be better. Foundation item: the National Basic Research Program (973) of China (No. 2005C13321804)     

Traffic Scheduling in WDM Passive Optical Network with Delay Guarantee

IntroductionWDM passive optical network (PON) is an at-tractive solution for future broadband access net-work in that it offers the potential of large capaci-ty, network security and data transparency[1]WDM PON connects the optical line terminal( OLT ) with multiple optical network units(ONU) through a splitter. The OLT has an arrayof m fixed-tuned transceivers, each tuned to a dif-ferent wavelength. Each ONU is equipped withone fixed transmitter (control channel) and onetunable trans…     

基于QoS升降级的无线单播多播混合带宽资源分配方法

在单播与多播混合服务的OFDM蜂窝系统中,因负载较重而使带宽资源被完全占用时,为接纳更多的多播用户,在单播多媒体用户可接受的范围内提出：基于信道容量平滑的QoS升降级带宽借用方法.通过建立QoS升降级的子载波借用模型和CUpDown-QoS算法,达到最大化多播用户数和减小多播切换呼叫中断率;提出了GoS保证下,限制新呼叫的动态带宽借用阈值,给出基于Markov模型的CBP（Call Blocking Probability）与HDP（Handoff Dropping Probability）最优折中的阈值确定方法,以及多播优先的动态带宽借用策略对阈值确定的影响.     

非均匀多业务分层网络的资源分配策略分析

研究一种支持多种业务(包括语音对话业务和数据流业务)的分层蜂窝网,在信道共享和信道分割 2 种资源分配策略下的网络性能.网络中的数据流业务根据当前的业务负载情况动态分配带宽,并通过双阈值带宽预留(DTBR)来保证不同业务的不同业务质量(QoS).实验数据显示了在不同业务量情况下2种资源分配方法的性能比较.     

A Distributed and adaptive framework for provisioning QoS in IPv6 networks

A distributed and adaptive framework （DAF） was proposed for provisioning quality of service （QoS） in IPv6 network. In DAF, per-flow admission control and resource reservation, in conjunction with a new IPv6 flow label mechanism, can be performed instantaneously in a fully distributed and independent fashion at the edge of network without hop-by-hop signaling. The flow label helps in resource reservation and packets forwarding for aggregated traffic on an edge-to-edge path basis. In addition, a bounded directional probing technique for DAF was designed to reconfigure resource reservation adaptively between every pair of edge router for aggregated traffic according to the fluctuation of its traffic load. The simulation results show that DAF provides QoS guarantees to individual flows with minimal overhead, as well as keeping the scalability characteristic like DiffServ.     

无线Mesh网络的跨层设计理论与关键技术

由于无线M esh网络(WMN)在拓扑、传输和业务上的特性,传统的用于有线网络的分层协议设计方法已不能保证其服务质量(QoS).探索基于物理层、MAC层、路由等协议层的WMN跨层设计方法的目标是在无线资源利用率和多媒体业务的QoS需求两方面达到较好的折衷.WMN各个协议层在设计过程中的有关协议和算法要求附加统一的跨层管理器,监测各层的分组传输性能或需求,动态控制或调节相关算法.通过实现较高协议层的多媒体业务QoS需求与较低协议层的网络状态信息在各协议层之间的共享,可以达到对协议层控制算法的优化.在合理地选择跨层设计目标的基础上,多个协议层需要联合设计与优化.从物理层、MAC层、路由协议层和TCP层等层面介绍了WMN跨层设计的一般原则和方法.归纳了目前WMN跨层设计中亟待深入研究的一些理论和关键技术,包括自适应速率与节能机制、基于QoS需求的跨层MAC协议设计和路由协议设计等.     

A Reliable Adaptive High-Definition Transmission System for Distance Learning

There is an increasing demand for supporting high-quality real-time audiovisual services for the next generation wired and wireless networks. However, due to variety of bandwidths of different networks, it is a great challenge for deployment. In this paper, a novel high-definition (HD) video transmission system was proposed which depends upon reliable compound multicast protocols and QoS control over the various kinds of networks. This system detects client's network condition and assigns it to a proper proxy. Each proxy is capable of detecting network parameters and adaptively tuning such transport parameters as bit rate, video resolution, frame rate and QoS mechanisms to this condition. It also provides FEC error recovery under consideration of characteristics of MPEG4 video codec. Our simulation demonstrates that different network clients such as ADSL, CERNET, and CERNET2 can receive more video reliability with less delay.     

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北京市自2006年至2009年以来在各类重大社会活动中应用了一系列交通需求管理策略. 本文重点研究了各项交通需求管理策略的目的和实施细节,详细对比了重大活动交通需求管理执行前后交通状态的变化. 研究结论表明,针对大型活动本身进行交通需求管理时需要充分发挥交通需求管理组合策略的效用;同时由于公众上班时间相对较为集中,所引发早高峰交通流的多变性和不确定性更容易造成交通拥堵,因此在设计大型活动期间交通管理措施时应对其投入更多的精力,提出具有针对性的方案解决其中潜在的问题.     

交通需求管理在武汉市跨江交通中的应用

针对武汉市跨江交通问题所采取的交通需求管理对策,以江汉一桥断交通封闭维修实施交通需求管理为实例,从城市的综合实力、可持续发展的角度,着重论述了武汉市要取得城市发展与交通发展的双赢,应该坚持同步实施交通需求管理。通过合理的交通政策、健康的土地利用方式等,均衡道路时空消耗,促进交通参与者的交通选择行为改变,诱导出行者最终放弃小汽车出行,从而选择运输效率高、环境污染低的公共交通,以取得交通供需平衡,支持城市社会、经济和环境的可持续发展。     

Two Bandwidth Packing Algorithms for the Centralized Wireless Network and Their Average-case Analysis

This paper presents a detail analysis of two bandwidth packing algorithms, used for processing connection requests in the centralized wireless network. Each call comes with a specific bandwidth request. A request can be satisfied only if there is sufficient bandwidth available during resource scheduling and allocation. Unsatisfied requests were held in a queue. The metric of bandwidth utilization ratio was used to quantify the performance of our algorithms. By theoretical analysis, our algorithms can improve the average bandwidth usage ratio significantly, about 8%~10% without adding much computation complexity. Moreover, our algorithms outperform next fit with fragmentation (NFF) algorithm when the bandwidth resource is scarce. In this paper, the contributions follows: Introducing bandwidth packing problem into wireless network; Proposing two new bandwidth packing algorithms for wireless network where the complicate scheduling algorithms are prohibited; Studying the average performance of our algorithms mathematically, which agree well with the simulation results.     

智能网联车辆混行交通流中灯语意图识别模型研究

为使混行交通流下智能网联车辆(Connected and Automated Vehicles, CAV)实现对人工驾驶车辆(Human-driven Vehicle, HV)前照灯灯语意图(Vehicle Headlights Intention, VHI) 的识别，弥补车对车(Vehicle to Vehicle, V2V)和鸣笛意图识别技术的不足，更好地与HV交互沟通，提出CAV对HV的VHI识别模型.模型包括：灯光感知、光数据处理、VHI识别3个模块，灯光感知模块通过RGB(Red-Green-Blue, RGB)和HSV(Hue-Saturation-Value, HSV)颜色空间感知前照灯(Vehicle Headlights, VH)，采用KLT(Kanade-Lucas-Tomasi Tracking，KLT)和车辆匹配算法定位跟踪发出灯语的HV；光数据处理模块采用光通道增益算法计算光辐射通量变化； VHI识别模块基于双层隐马尔可夫模型(Double-layer Hidden Markov Model，DHMM)辨识VH 闪烁次数和HV行驶状态，实现VHI识别.在3种灯语示意典型场景下的实验结果表明：1 s内 VH感知准确率为96.8%，定位跟踪精度小于1°，VHI识别率为96.6%，满足混行交通环境下 CAV对HV驾驶意图的识别要求，基本保证实时性，为混行交通流中CAV自动驾驶决策提供理论依据.     

交通需求管理及其在中国的应用

交通需求管理 ( TDM)是发达国家已经广泛研究、试验和实施的一项旨在解决目前交通问题的有效措施。综合分析了 TDM在几个典型发达国家的应用情况及其经验 ,初步分析了该措施在中国应用的可行性 ,认为目前不能全面引入 TDM措施 ,但需要在大力发展的交通规划与管理中引入 TDM思想 ,并以此作为长远的发展目标     

智能网联车辆混行交通流中灯语意图识别模型研究

为使混行交通流下智能网联车辆(Connected and Automated Vehicles, CAV)实现对人工驾驶车辆(Human-driven Vehicle, HV)前照灯灯语意图(Vehicle Headlights Intention, VHI) 的识别，弥补车对车(Vehicle to Vehicle, V2V)和鸣笛意图识别技术的不足，更好地与HV交互沟通，提出CAV对HV的VHI识别模型.模型包括：灯光感知、光数据处理、VHI识别3个模块，灯光感知模块通过RGB(Red-Green-Blue, RGB)和HSV(Hue-Saturation-Value, HSV)颜色空间感知前照灯(Vehicle Headlights, VH)，采用KLT(Kanade-Lucas-Tomasi Tracking，KLT)和车辆匹配算法定位跟踪发出灯语的HV；光数据处理模块采用光通道增益算法计算光辐射通量变化； VHI识别模块基于双层隐马尔可夫模型(Double-layer Hidden Markov Model，DHMM)辨识VH 闪烁次数和HV行驶状态，实现VHI识别.在3种灯语示意典型场景下的实验结果表明：1 s内 VH感知准确率为96.8%，定位跟踪精度小于1°，VHI识别率为96.6%，满足混行交通环境下 CAV对HV驾驶意图的识别要求，基本保证实时性，为混行交通流中CAV自动驾驶决策提供理论依据.     

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综合评述了活动－出行行为研究方法和存在的问题,引入贝叶斯结构学习和参数估计方法,辅以基于活动的出行行为分析理论、非集计建模方法和SP/RP数据融合方法,提出了基于贝叶斯结构学习和参数估计方法的出行行为与TDM策略互动关系分析方法的框架,探索了改进已有研究方法的途径。研究表明,贝叶斯理论可以将居民的个人属性及隐性非样本信息在出行行为预测中充分表达,并解决MNP等复杂非集计模型的参数标定问题。将贝叶斯理论与已有的出行行为分析方法相结合,可以使出行行为预测更为精确、全面和灵活,从而更加准确地描述活动－出行决策行为与TDM策略的互动响应关系,为制定有效的TDM策略,缓解城市交通供需矛盾提供理论依据。     

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奥运期间小汽车限行政策的实施,有效缓解了北京道路交通拥堵。本文通过措施实施前后收集的居民入户调查数据,定量分析了限行措施对居民出行特征的影响,研究发现：限行政策实施后,居民总体出行率由1.88次/日降低到1.70次/日,上下学、接送人和工作外出等出行比例明显降低;私人机动车出行强度降低0.07次/（天&;#8226;辆）,乘载率提高0.10人/车;公务车出行强度增加0.70次/（天&;#8226;辆）,乘载率提高0.32人/车;地铁、公交和小汽车出行时耗分别缩短了12 min,8 min和8 min。     

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智能运输系统(ITS)是当前解决交通问题的最佳途径之一,而动态交通信息的发布与预测是ITS的关键所在。然而由于在各种外部因素下,道路交通状态呈现出随机变化的特性使得动态交通信息的发布与预测成为一大难点。结合某城市的实际情况,本文建立了在定位误差、采样间隔、车辆类型、道路类型等因素影响下的行程车速估计模型,并用实测数据对模型进行精度验证。结合出租车车辆的特殊信息,改进了低采样频率浮动车技术的估计算法,建立了空车数据处理模型;针对城市复杂和相似路段问题,提出了基于距离、方向角、连通性、历史数据以及车流方向等约束条件下的地图匹配算法;针对低采样频率浮动车数据,提出了考虑交叉口影响下的行程车速估计算法,通过实测数据评估了算法的性能;最后,针对不同检测技术的特征,提出了数据融合算法。     

构筑大都市区一体化综合交通体系论TDM的应用

结合我国城市化进程及由此产生的对交通系统的需求特点。提出应构筑大都市区一体化综合交通体系。据此，对建设我国大都市区一体化综合交通体系的目标进行了分析，井重点探讨了在构筑一体化综合交通体系过程中对TDM（交通需求管理）的应用以及这种应用的有效性。     

Pre-emptive channel borrowing and traffic overflowing channel allocation scheme for multimedia overlay networks

This paper proposes a channel allocation scheme for multimedia wireless networks, in which a twolayer macro-cell or micro-cell architecture is considered. Macro-cells are used to access high-mobility services; while micro-cells, which are overlaid by the macro-cells, are used to cater low-mobility services. To analyze the scheme, a multidimensional Markov traffic model is firstly developed, in which traffic characteristic of two special periods of time is considered. And then, a pre-emptive channel-borrowing scheme combined with trafficoverflowing strategy for multimedia (voice, video or data) networks is proposed, in which handoff requests can not only borrow channels from adjacent homogenous cells, but also be overflowed to heterogeneous cells. Priority strategies are also dedicated to high-mobility services for they can pre-empt channels being used by low-mobility services in macro-cells. To meet the high quality of service (QoS) requirements of video services and increase the channel utilization ratio, video services can be transformed between real-time services and non-real-time services as necessary. Simulation results show that our schemes can decrease the blocking probabilities and improve the channel utilization.     

基于TDM的出租车供需调控方案研究

交通需求管理（TDM）是能从根本上解决城市交通问题的策略,具有现实的意义。针对成都市出租车供需现状,运用系统的思想对各供需调控方案进行评价比选,分析交通需求管理的必要性并提出针对出租车的交通需求管理的具体措施,可为解决出租车的供需矛盾提供参考。     

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交通需求管理（TDM）已成为保障奥运会期间突增交通需求的必要手段。本文在综合奥运会交通需求特性和对比往届奥运会TDM政策要点的基础上,从控制机动车使用、设置奥运专用道、公共交通保障、错时上下班及人性化保障等5个方面阐述TDM政策在北京奥运会中的应用,并从政策综合性、可操作性、接受程度及政策实施效果等4个角度对该TDM政策进行效果评价。数据表明：TDM政策的实施使道路交通流量下降22.5%,早高峰路网平均车速提高28.5%,122报警量下降,公共交通客运量大幅上升,且公共交通的出行比例达45%以上,有效均衡了交通需求,达到预期目标。