无线多媒体传感器网络互层技术研究

无线多媒体传感器网络(WMSNs)是一种能在任何地方获得环境中诸如视频和音频流、静止图像和标量传感数据的无线互联设备的网络.大信息量的多媒体数据的采集与处理,在军事、民用和商业领域中具有广阔的应用前景.由于无线网络的特性,互层技术被广泛应用于无线网络的协议设计中.针对WMSNs互层技术的最新国内外研究状况进行了调查、归纳和总结,并且就其中各方面有待研究的问题进行了讨论.     

基于多媒体业务的无线网络跨层优化与仿真

由于无线信道的时变衰落特性以及不同用户对服务质量(QoS)的动态要求,传统的无线网络协议栈分层设计思想难以满足未来移动通信系统的需求.提出一种基于多用户公平性准则的跨层优化设计方法以解决该问题.基于多用户无线传输环境下的多媒体业务特性,联合物理层,数据链路层和应用层进行参数提取和优化设计,从应用层角度出发,提出了该跨层设计准则.在保证用户间的公平性同时最大化各用户观察到的视频流质量,充分有效地利用了无线资源.仿真结果表明跨层优化准则能同时很好地改善用户间的公平性和系统整体性能.     

无线视频传输中MPEG-4自适应分包算法

MPEG-4视频流在无线信道中传输时，视频数据必须符合一定的结构，以便当信息丢失和比特错误时，能够进行差错控制。将视频净载荷按一定结构进行适当分组的处理称为打包或者分包。该文对分包的理论模型进行了分析，提出了一种兼顾封装效率和图像质量的自适应分包算法，并利用实时传输协议在GPRS无线信道中进行传输，取得了理想的视觉效果。     

Classification-Based System For Cross-Layer Optimized Wireless Video Transmission

Joint optimization strategies across various layers of the protocol stack have recently been proposed for improving the performance of real-time video transmission over wireless networks. In this paper, we propose a new, low complexity system for determining the optimal cross-layer strategies for wireless multimedia transmission based on classification and machine learning techniques. We first determine offline the optimal cross-layer strategy for various video sequences and channel conditions (training data). Subsequently, we extract relevant and easy to compute content features, encoder-specific parameters, and channel resources from the training data, and train a statistical classifier based on these optimal results. At run-time, we predict using the classifier the optimal cross-layer compression and transmission strategy using these simple, on-the-fly computed features. Hence, we consider the complex problem of finding the optimal cross-layer strategy during the training phase only, and rely at transmission-time on low-complexity classification techniques. We illustrate the proposed classification-based system by performing MAC-application layer optimizations for video transmission over 802.11a wireless LANs. Specifically, we predict the optimal MAC retry limits for the various video packets and compare our results against both optimal and conventionally used ad-hoc cross-layer solutions. Our results indicate that considerable improvements can be obtained through the proposed cross-layer techniques relying on classification as opposed to optimized ad-hoc solutions. The improvements are especially important at high packet-loss rates (5% and higher), where deploying a judicious mixture of strategies at the various layers becomes essential. Furthermore, our proposed classification-based system can be easily modified to include other layers from the OSI stack during the cross-layer optimization.     

Cross-Layer Error Control for Multimedia Streaming in Wireless/Wireline Packet Networks

In this paper, we propose a cross-layer error control framework for robust and low delay multimedia streaming in tandem-connected IEEE 802.11 wireless LANs and the Internet. For this network configuration, we model the end-to-end delay and packet loss rate as a function of the automatic repeat request (ARQ) and forward error correction (FEC) error control mechanisms that are employed at the application and wireless link layers. The analytical model is used as the basis of a delay-constrained error control algorithm that adapts the protection level at the application and link layers so that the end-to-end packet loss rate is minimized. With extensive simulations, we validate the efficiency of the proposed cross-layer error control methodology for delay-sensitive pre-compressed video streaming.      

A Cross-Layer Analysis of Session Setup Delay in IP Multimedia Subsystem (IMS) With EV-DO Wireless Transmission

This paper analyzes the session setup delay in the IP multimedia subsystem (IMS) with the CDMA2000 evolution data only rev. A (EV-DO rev. A) standard for wireless transmission. Session setup delay is particularly critical for interactive multimedia applications, such as gaming, push-to-X and voice over IP (VoIP), as it directly translates in user perception of service quality. Keeping signaling delay low, however, is a challenge in IMS due to the text-based nature of the session initiation protocol (SIP) for signaling, and, more significantly, due to the lossy and capacity constrained wireless links. To address this challenge, we analyze the session setup delay end-to-end, by taking into account key system properties across all layers, ranging from radio links to IMS signaling architecture. We present a model for cross-layer performance analysis and simulation, which includes the statistical properties of the EV-DO (rev. A) wireless channel, and also takes into consideration the properties of transport protocols (TCP, UDP) and SIP signaling (message size and compression). By means of analysis and simulations, we study the setup delay performance of a generic, multi-operator IMS communication scenario between two mobile users. We describe how session setup delay can be estimated and reduced in realistic IMS settings and we propose architecture alternatives to the basic IMS scenario. The results derived from this study show that the proposed methods can incrementally lead to a lower setup delay and less sensitivity to the radio transmission quality and frame error rate compared to the base IMS scenario     

延迟敏感的移动多媒体会议端到端服务质量保障

随着异构无线网与智能移动终端的快速发展,移动多媒体会议逐渐成为重要的网络应用.然而,在不可靠、多变的无线网络环境下,因传输单向延迟过长所造成的多媒体视频丢帧、跳帧、断续等现象严重影响会议的服务质量和用户体验.文中提出一种应用层端到端服务质量保障方法.该方法将数据包分段重组与异构无线网路径分集传输相结合,在考虑带宽、延迟、权重以及长度等多种参数情况下对视频数据包分段并发送,各分段经路径分集传输到达客户端、通过有效性检验后进行重组.文中为实现该方法,设计了一种服务器-客户端形式多路径数据包调度算法,构建端到端虚通路保障视频流的快速传输.实验数据表明,此方法能够有效地整合异构无线网带宽,减少传输单向延迟.     

无线传感器网络中能量均衡延迟敏感的节点调度方案

在无线传感器网络中,为了节省能量,许多方案使用让节点工作一段时间就休眠一段时间的工作周期(duty-cycle)的模式,但节点的休眠会引发很大的网络延迟.所以既要使用工作周期的模式来节能又能让网络获得较小的延迟,一直是人们研究的热点及难点问题.为了既能获得较小的网络延迟又能增大网络的生命周期,论文提出了一种能量均衡延迟敏感(Energy-Balance and Delay-Sensitive,EBDS)的节点调度算法,在选择下一跳的时候,通过在规定的时间阈值内,选择醒着的最短路径上的节点来减小网络延迟,或是选择剩余能量最大的节点实现能量均衡来增大网络生命周期作为下一跳,这样可以把网络延迟控制在一定的范围内的同时增大网络的生命周期.理论分析及实验结果表明,与现有的研究相比,EBDS能够较好的把延迟控制在可接受范围内的同时有效地增大网络的生命周期.     

能量有效和延迟敏感的无线传感器网络数据收集协议

利用移动Sink进行数据收集是无线传感器网络数据收集的一个趋势。本文提出一种能量有效、延迟敏感的移动数据收集协议（Energy—efficient and Delay—Sensitive Data Gathering Protocol for Wireless Sensor Networks,简称EEDS）。EEDS中,移动Sink在网络中穿行,从代理节点收集传感器节点监测到的数据。为了减少数据收集的延迟,采用类TSP（Traveling Salesman Problem）的解决方法,确保移动Sink在各个代理节点中收集数据时,始终选择一条最短路径在网络中行走。模拟仿真表明,提出的数据收集协议在延长网络生命周期以及减少数据收集延迟方面都有显著的优势。     

嵌入式多媒体图象无线传输系统的设计

本系统由硬件和软件两部分组成,硬件部分采用Mm9微处理器作为控制器,通过选择合适外围芯片,实现了外围电路的扩展,视频采集模块为中星微摄像头,无线传输模块采用高速无线网卡,软件部分操作系统采用Microsoft公司的嵌入式系统winCE,该操作系统采用模块化设计,简单实用.通过程序设计,实现对像头的开启,初始化,采集,关闭等控制操作,最后实现了图象的无线传输.     

基于ARM-Linux的无线音视频传输系统

本文设计了一种基于S3C2410X微处理器、Linux操作系统的无线多媒体传输系统.论文首先介绍了系统的结构功能设计;接着给出了嵌入式无线音视频传输系统软硬件设计方案,包括系统发送端硬件结构设计和接收端硬件结构设计,并且给出了各个功能模块的芯片选择;最后,以嵌入式Linux操作系统为软件平台,WLAN为传输媒介的平台构架和环境搭建,设计并且实现了嵌入式无线音视频传输系统应用程序.     

无线网状网跨层路由的研究

目前,无线网状网跨层路由设计方兴未艾,以往无线路由设计是基于最小跳数的,缺少对无线网状网特性的综合考虑,并不能充分发挥出无线网状网的优势。该文提出了基于"队列负载率"和"链路传输效率"的跨层路由协议算法,通过将MAC层的网络状态信息传递给网络层的路由代理,以便选择负载较小的最佳路由。通过仿真可以发现,改文提出的路由不仅显著提高了吞吐量,而且使包的投递更加可靠,提高了QoS。     

无线网络多媒体传输拥塞控制机制研究

本文针对无线局域网环境对多媒体信息传输过程中丢包状况区分不理想的情况,提出了在TFRC 协议基础上的一种改进,添加了丢包区分机制spike,同时采用了TFRC 协议的基于公式的速率控制机制,改进后的协议,既具备了TFRC 协议的TCP 友好性,又具有精确区分丢包的能力,仿真结果表明,具有丢包区分机制的改进型算法更适合无线网络环境下的多媒体传输。     

Coordinated Handover Initiation and Cross-Layer Adaptation for Mobile Multimedia Systems

A cross-layer mechanism to improve the performance of real-time applications over IEEE 802.16e metropolitan area networks is presented. The proposed mechanism uses channel quality and service quality information from the physical and medium access control layers, respectively, to determine the most suitable burst profile, transmission power level and media encoding rate for a connection, or even initialize a handover execution. The main contribution of this mechanism is the integration of the handover initiation into the cross layer logic, aiming to improve the overall system performance. Extensive simulation results show that the proposed mechanism offers significant performance improvement in terms of packet loss rate, power consumption, throughput, and system capacity.     

基于MB-OFDM UWB的短距离无线多媒体传输

超宽带（UWB）是实现高速无线个域网（WPAN）多媒体传输的关键技术。UWB以超短周期脉冲进行调制，并使用超宽的RF频谱带宽传递数据，可通过重叠的原则共享已占用的频谱资源；其具有频谱利用率高、抗多径衰落能力强、发送功率极小、系统安全性好等特点。UWB可为消费类电子设备提供高速无线连接解决方案，使视频连接和桌面应用等能在通用射频平台上运行。因此，研究UWB的标准化、产品化与市场化进程，剖析其主流技术。对于制订我国相关标准，促进UWB技术与系统产品在中国的发展和实施，具有积极的现实意义。为使UWB主流技术能被进一步了解，在跟踪研究UWB标准化的基础上，分析了作为国际上第1个商用UWB标准的多频带正交频分复用（MB—OFDM）方案的原理与技术特征，并阐述了基于该方案的无线多媒体超宽带（WiMedia UWB）平台与应用环境，产品整合进展及应用前景．     

Special Issue on Quality-Driven Cross-Layer Design for Multimedia Communications

The 14 papers in this special issue are divided into four categories: theoretical frameworks and schemes; integration of media processing and network protocols; heterogeneity; and quality evaluation.     

基于匹配理论的无线广播编码重传算法

针对成批数据在无线广播过程中发生丢包后的重传策略,利用网络编码技术,研究尽可能多地减少重传次数的方法.首先通过矩阵及向量的运算给出了待重传数据满足编码条件的代数表达形式,再根据关联矩阵构造相应的图,最后通过图论中的最佳匹配理论给出了一种寻找编码机会的优化算法.此算法中不但能够找出最多的两两编码机会,而且还考虑了将尽可能多的数据包编在一起的可能性,从而尽可能地减少了重传次数,实现了编码的优化,有效提高了网络带宽效率和吞吐量.     

An Effective Error Resilient Packetization Scheme for Progressive Mesh Transmission over Unreliable Networks

When a 3D model is transmitted over a lossy network,some model information may inevitably be missing. Under such situation,one may not be able to visualize the receiving model unless the lost model information has been retransmitted. Progressive model transmission offers an alternative to avoid the "all or nothing situation" by allowing a model to be visualized with a degraded quality when only part of the model data has been received. Unfortunately,in case some model refinement information is missing,one may still need to wait for such information to be retransmitted before the model can be rendered with a desired visual quality. To address this problem,we have developed a novel error resilient packetization scheme. We first construct a Non-Redundant Directed Acyclic Graph to encode the dependencies among the vertex splits of a progressive mesh. A special Global Graph Equipartition Packing Algorithm is then applied to partitioning this graph into several equal size sub-graphs,which is packed as packets. The packing algorithm comprises two main phases:initial partition phase and global refinement phase. Experimental results demonstrate that the proposed scheme can minimize the dependencies between packets. Hence,it reduces the delay in rendering 3D models with proper quality at the clients.     

基于3G无线网络的多媒体传输关键技术研究

由于3G无线网络具有高丢包率、信道带宽有限且不稳定等特点,使用传统可靠的TCP协议传输视频,往会造成无线信道拥塞,出现画面延迟长、抖动严重等问题。而使用简洁、实时性更好的UDP协议传输视频,容易造成大量的数据丢失,大大降低视频的质量。针对上述出现的问题,提出了一种结合自适应的加权平均码率传输控制机制和基于TCP/UDP混合协议的视频帧分级传输模型的传输技术,使得视频传输的实时性和画面质量都能达到一个比较好的表现。