AIFS 区分的IEEE 802.11e EDCA 吞吐率分析模型与自适应MAC 算法

针对IEEE 802.11e EDCA(enhanced distributed channel access)支持业务区分服务的特点,提出了一个基于AIFS(arbitration inter-frame space)区分的信道吞吐率分析模型,该模型将不同接入等级的业务统一到一个信道模型中进行分析.通过数值计算结果与仿真实验结果的对比,验证了该模型的准确性,尤其是在分析信道吞吐率方面更优于Xiao 的Markov 链模型.根据提出的分析模型,研究了近似优化条件,使得各类优先级业务的发送概率平衡虚拟发送时间段中空闲时间与冲突持续时间对系统性能的影响,实现靠近最优的信道吞吐率,从而使计算复杂度大为减小.利用数值分析的方法验证了近似优化条件实现靠近最优信道吞吐率的可行性.最后,提出的DPS(dynamicparameter-tuning scheme)算法根据负载情况自适应地调整不同级别业务的相应参数,使得系统时时满足优化条件,在各种场景下都能实现最大信道吞吐率,同时又满足EDCA 支持QoS 区分的要求.仿真结果验证了DPS 算法不仅能够根据竞争节点的数目变化对信道吞吐率进行优化,而且其性能也明显优于标准的IEEE 802.11e EDCA 机制.     

面向QoS区分的自适应状态转移概率动态更新算法

为了提高在大规模、重负载环境下IEEE 802.11e EDCF(Enhanced Distributed Coordination Function)机制的网络性能.引入了在信道空闲时退避计数器状态转移概率的概念,提出一种新的提高网络QoS(Quality of Service)的方法—根据当前网络状态,动态地调节不同优先级在信道空闲时退避计数器的状态转移概率.通过马尔科夫链数学模型验证了在饱和情况下所提算法的优越性,并推导出了状态转移概率的最优值,给出了实现此算法的基本流程和步骤.实验结果表明,此算法不仅保证了各种优先级业务之间的公平性,而且显著提高了网络吞吐量,同时降低了MAC层延时和丢包率.结果验证了在负载动态变化时,算法的自适应性和优越性.     

基于自适应蚁群算法的多受限网络QoS路由优化

高速多媒体网络中的路由问题是有QoS约束的路由问题,多受限的路由问题是一个NP-完全问题。该文提出了一种解决多受限QoS路由问题的自适应蚁群算法。该算法采用基于目标函数值的信息素分配策略和根据目标函数值自适应调整蚂蚁的搜索行为,从而保证搜索的快速有效性,使多受限QoS路由优化问题得到很好地解决。     

基于蚁群算法的移动自适应网QoS路由算法

在移动自适应网中,由于无线环境的不稳定性及终端的移动性造成网络拓扑结构不断变化,使网络中端对端的服务质量随时间不断变化.为移动自适应网提供服务质量保证的关键是移动自适应网的QoS路由问题.提出了一种适用于移动自适应网的QoS路由算法.该算法将蚁群算法与移动自适应网的特点相结合,可以高效地在该网络中寻找满足延迟、延迟抖动、带宽、包丢失率、节点跳数和费用等多项指标的QoS路由,从而显著地提高移动自适应网的QoS路由性能.     

基于自适应变异蚁群算法的QoS路由算法

多约束QoS单播路由问题是NP完全问题,针对基本蚁群算法在解决该问题时易于陷入局部最优、收敛速度慢的缺点,提出自适应变异蚁群算法对该问题进行求解。该算法采取自适应变异方法,引入二次蚁群搜索机制,减少了算法陷入局部极值的可能性,提高了算法的寻优能力和收敛速度。仿真实验结果验证了该算法的可行性和有效性。     

自适应MAC的改进算法

针对具有欠阻尼特性的被控对象，提出了自适应MAC的改进算法。改进算法采用一种紧凑模型描述对象单位脉冲响应序列，可使截取为内模的对象单位脉冲响应有限序列长度大大减小。因此，内模在线辨识及MAC的在线计算量显著减小，大大提高了自适应MAC的实时性。     

VoWLAN的MAC层QoS改进算法研究

竞争窗口及其退避算法是影响QoS的重要因素之一。本文以EDCF算法和它的改进算法AEDCF为基础,提出了一种新的动态改进竞争窗口的算法N-EDCF,根据网络冲突率和阈值来划分网络状态,然后对不同的网络状态选用不同的竞争窗口和退避算法。仿真表明,N-EDCF优化了VoWLAN的QoS性能。     

一种细粒度的区分服务及QoS映射优化研究

针对传统区分服务模型服务等级分类有限,结合策略管理的优势,提出了基于策略的细粒度区分服务概念,给出了不同类型区分服务的通用描述形式,提出了基于遗传算法的细粒度服务优化算法.当系统资源不足以满足多媒体流的传输要求或者用户需要细粒度的区分服务质量时,通过启用遗传算法对PHB进行组合优化,能够在较少的代数内求得满足用户QoS要求的最优解,实验表明该算法可行.     

IEEE 802.11支持QoS区分服务的性能优化

基于IEEE 802。11 p-persistent协议模型的研究,对一种近似优化条件在多优先级业务网络条件下的适用性进行了证明。应用该近似优化条件,提出了一种适用于IEEE 802。11 QoS区分服务支持的自适应优化算法QATC (QoS-supporting adaptive transmission control)。算法利用信道侦听信息实时优化调整各优先级业务的发送概率,更新相应的协议参数,实现信道利用率的提高和系统性能的增强。QATC算法不需要估计各优先级业务的节点数量,并且拥有     

QoS动态路由算法分析

保证服务质量(QoS）的通信是当今网络发展的必然趋势之一。动态路由算法可根据网络拓扑和负载情况实时为业务选择路径。其合理性和有效性对于网络资源的优化使用及网络运行性能起着重要作用。文章阐述了QoS动态路由算法的研究内容：链路量度的选择、选路原则、改进Bellman-Ford算法和Dijkstra算法以及算法的触发,并总结了QoS路由算法目前存在的几个问题。     

改进的动态p-坚持CSMA协议

通过研究p-坚持CSMA协议发送概率的动态调整算法,提出一种动态p-坚持CSMA协议。在该协议中,发生冲突重传时的发送概率并非固定不变,而是关于冲突重传次数的函数。通过建立二维马尔可夫链模型,进行理论推导并分析归一化系统饱和吞吐量的性能,结果表明,与p-坚持CSMA相比,动态协议的性能更优。     

无线信道视频流编码与自适应传输方案

由于无线信道的时变特性和移动设备有限的能量资源,保证无线网络视频流传输的Qos是一项比较困难的任务。文章提出了一种基于无线网络的视频流自适应传输架构。这个架构不仅动态的估计了无线网络的状态进行自适应传输,而且同时执了差错控制和功率控制。通过分析网络的状态和视频流的特性来动态分配资源,提高了端到端的QoS。     

一种结合业务区分的S-MAC协议

针对无线传感器网络中S-MAC协议没有考虑网络的QoS性能问题,本文提出了一种结合业务区分的S-MAC协议,令优先级不同的节点获得不同的接入信道概率,提高了传感器网络的QoS性能。仿真结果显示,改进后的S-MAC协议确实提高了网络的QoS性能。     

具有QoS功能的视频传输系统的实现

首先提出了QoS视频传输系统的必要性;然后介绍了QOS的体系结构及应用现状;接着,设计实现了一个实用的具有QoS功能的视频传输系统并介绍了该系统组成部分的功能模块;最后指出,该系统在实际应用方面作出了很好的尝试,具有较好的实用价值。     

基于蓝牙的连续媒体实时传输技术的研究

由于蓝牙无线信道带宽较窄且动态变化，在其上实时传输连续媒体数据是一个巨大挑战．本文研究了其中若干关键技术．包括蓝牙通信技术、视频／音频压缩技术和自适应服务质量控制技术等．文中提出了一种基于简单网络管理协议(SNMP)的自适应服务质量控制方案．设计了蓝牙多媒体传输管理信息库(简称BMT—MIB)，通过动态监测当前蓝牙无线信道和终端系统状态，有效利用带宽等资源．文中还给出了基于蓝牙的远程监控系统原型的设计和实现。     

A QoS-Enabled Transmission Scheme for MPEG Video Streaming

While MPEG is the de facto encoding standard for video services, online video streaming service is becoming popular over the open network such as the Internet. As the performance of open network is non-predictable and uncontrollable, the tuning of the quality of service (QoS) for on-line video streaming services is difficult. In order to provide better QoS for the delivery of videos, there are proposals of new encoding formats or new transmission protocols for on-line video streaming. However, these results are not compatible with popular video players or network protocols and hence these approaches are so far not very successful. We use another approach which tries to by-pass these problems. We designed a QoS Tuning Scheme and a QoS-Enabled Transmission Scheme for transmitting MPEG videos from video servers to clients. According to the traffic characteristics between the video server and each individual client, the QoS Tuning Scheme tunes the QoS to be delivered to each individual client on the fly. Furthermore, our QoS-Enabled Transmission Scheme can be applied over any protocol, such as HTTP which is the most popular protocol over the open network. With our transmission scheme, bandwidth can be better utilized by reducing transmitted frames which would have missed their deadlines and would eventually be discarded by the clients. This is achieved by sending frames according to their impact on the QoS in the playback under the allowed throughput. With these schemes, users can enjoy video streaming through their favorite video players and with the best possible QoS. In order to facilitate the real time QoS tuning, a metric, QoS-GFS, is developed. This QoS-GFS is extended from the QoS-Index, another metric which has taken human perspective in the measurement of video quality. Hence QoS-GFS is better than the common metrics which measures QoS by means of rate of transmission of bytes or MPEG frames. We designed and implemented a middleware to perform empirical tests of the proposed transmission scheme and QoS tuning scheme. Experiment results show that our schemes can effectively enhance the QoS for online MPEG video streaming services. The work reported in this paper was supported in part by the RGC Earmarked Research Grant under RGC HKBU 2074/01E, and by the FRG under FRG 00-01/I. Joseph Kee-Yin Ng received a B.Sc. in Mathematics and Computer Science, a M.Sc. in Computer Science, and a Ph.D. in Computer Science from the University of Illinois at Urbana-Champaign in the years 1986, 1988, and 1993, respectively. Dr. Ng is currently an associate professor in the Department of Computer Science at Hong Kong Baptist University. His current research interests includes Real-Time Networks, Multimedia Communications, Ubiquitous/Pervasive Computing, Mobile and Location-aware Computing, Performance Evaluation, Parallel and Distributed Computing. Dr. Ng is the Technical Program Chair for TENCON 2006, General Chair for The 11th International Conference on Embedded and Real-Time Computing Systems and Applications (RTCSA 2005), Program Vice Chair for The 11th International Conference on Parallel and Distributed Systems (ICPADS 2005), Program Area-Chair for The 18th & 19th International Conference on Advanced Information Networking and Applications (AINA 2004 & AINA 2005) and he had served as the General Co-Chair for The International Computer Congress 1999 & 2001 (ICC'99 & ICC'01), the Program Co-Chair for The Sixth International Conference on Real-Time Computing Systems and Applications (RTCSA'99) and the General Co-Chair for The 1999 and 2001 International Computer Science Conference (ICSC'99 & ICSC'01). Dr. Ng is a member of the Editorial Board of Journal of Pervasive Computing and Communications, Associate Editor of Real-Time Systems Journal and Journal of Mobile Multimedia. He is a guest editor of International Journal of Wireless and Mobile Computing for a special issue on Applications, Services, and Infrastructures for Wireless and Mobile Computing. Dr. Ng is currently the Region 10 Coordinator for the Chapter Activities Board of the IEEE Computer Society, and is the Coordinator of the IEEE Computer Society Distinguished Visitors Program (Asia/Pacific). He is a senior member of the IEEE and has been a member of the IEEE Computer Society since 1991. Dr. Ng has been an exco-member (1993–95), General Secretary (1995–1997), Vice-Chair (1997–1999), Chair (1999–2001) and is the immediate past Chairman of the IEEE, Hong Kong Section, Computer Chapter. Dr. Ng received the Certificate of Appreciation for Leadership and Service (2000–2001) from IEEE Region 10 and the IEEE Meritorious Service Award from IEEE Computer Society at 2004. He is also a member of the IEEE Communication Society, and ACM. Karl R.P.H. Leung received his Ph.D. from The University of Hong Kong. He is currently a Principal Lecturer in the Department of Information and Communications Technology at the Hong Kong Institute of Vocational Education (IVE). He is the founder of the Compuware Software Testing Laboratory in the IVE with a donation from the Compuware Asia Pacific Co. Ltd. His research areas include: domain modeling, mission critical software engineering methodology, secure workflow systems, GSM-based location estimation, and QoS of MPEG streaming. He is a Senior Member of the IEEE and IEEE Computer Society, and has held major office of the IEEE Hong Kong Section Computer Chapter. While he was the chairman in 1998, the Chapter won the IEEE Most Outstanding Computer Society Chapter Award. He is also a Chartered Engineer of Engineering Council (UK), a Chartered Information Systems Engineer of British Computer Society (UK), an Engineer of Hong Kong Institution of Engineers, Registered Professional Engineer (Information) of Hong Kong Engineers Registration Board, and a member of ACM, BCS, ACS, HKIE and HKCS. Calvin Kin Cheung Hui received a B.Sc. (First Class Honours) in Computer Science, and a M.Phil. degree in Computer Science from Hong Kong Baptist University in the years 1999, and 2002, respectively. Mr. Hui's research interests includes Real-Time Networks, VoD Systems, Video Streaming, Multimedia Communication, and Distributed Systems Performance Evaluation.     

具有QoS功能的视频传输系统的实现

首先提出了QoS视频传输系统的必要性；然后介绍了Qos的体系结构及应用现状；接着，设计实现了一个实用的具有QoS功能的视频传输系统并介绍了该系统组成部分的功能模块；最后指出，该系统在实际应用方面作出了很好的尝试，具有较好的实用价值.     

一种结合业务区分的S-MAC协议

针对无线传感器网络中S-MAC协议没有考虑网络的QoS性能问题,本文提出了一种结合业务区分的S-MAC协议,令优先级不同的节点获得不同的接入信道概率,提高了传感器网络的QoS性能。仿真结果显示,改进后的S-MAC协议确实提高了网络的QoS性能。     

一个基于分层结构的Ad Hoc网络路由协议

分层结构已经被引入到有线网络。然而，由于在Ad Hoc网络中所有的终端都是移动的．所以引入分层结构很困难。解决此问题，本文提出了一个基于自治分簇策略的新型分层路由协议：Hi-TORA。Hi-TORA包含分簇策略和节点间的路由协议，它应用了TORA的思想，但也有所不同。在文章最后，对Hi-TORA和DSDV、DSR、ZRP、TORA等协议做了比较。