机会网络中基于摆渡节点与簇节点相互协作的路由机制

机会网络是一种不需要在源节点和目的节点之间存在完整路径,利用节点移动带来的相遇机会实现网络通信的延迟容忍自组织网络,它以“存储-携带-处理-转发”的模式进行.为实现互不相交簇间的信息传输,本文设计了一种带阈值的簇移动模型CMMT,并提出了一种基于摆渡（Ferry）节点与簇节点协作的路由算法（CBSW）.该算法减少了冗余的通信和存储开销,以及在Spray阶段簇节点没有遇到目的节点或摆渡节点,进入Wait阶段携带消息的节点采用直接分发方式只向目的节点传输等问题.仿真实验表明,CBSW算法能够增加传输成功率,减少网络开销和传输延迟.     

融合时空域变化信息的视频感知哈希算法研究

感知哈希(Perceptual Hashing)是多媒体数据集到摘要集的单向映射,为多媒体数字内容的标识、检索、认证等应用提供了安全可靠的技术支撑.本文提出一种融合视觉感知及时空域特征的视频感知哈希算法.算法首先对视频序列每一帧进行随机可重叠分块,并计算每个分块以像素为单位的亮度均值,在某一步长下,以同一帧的分块亮度差作为视频帧空域特征,以不同视频帧相同位置的分块亮度差作为时域特征,通过哈希量化得到时空域感知哈希,通过时空域感知哈希融合,最后得到简洁的视频唯一标识——摘要哈希.实验结果表明,该算法表现出较好的鲁棒性与区分性,通过相似度拟合图算法分析,可以实现视频篡改的准确检测及定位.     

基于移动设备UAProf的通用多媒体访问技术

通用多媒体访问UMA指的是任何用户在任何时间和地点，使用任何设备通过任何网络访问任何多媒体内容的能力．它提供了一种当用户试图访问他们的选择而不考虑所持终端特性和通信网络结构的一种调整传输内容的方法：用户代理UAProf是描述和交换有关移动终端能力信息用户偏爱的标准。本文在描述UAProf规范的基础上，介绍了三种获取客户端UAProf信息的方法，提出了一种服务器端根据UAProf信息调整多媒体内容以满足客户端性能的框架与机制。     

基于4G网络的移动多媒体传输关键技术

针对3G网络在移动状态下传输高清视频画面会遇到画面质量差、卡阻等现象的问题,对4G网络移动多媒体传输进行了简要介绍。依托快速发展的4G网络,通过集成视频压缩、网络传输等关键技术,详细计算得出移动高清视频经过视频编码标准H.265压缩后可以在4G网络下高质高速的传输。在此基础上,构建了视频传输系统实现方案,重点阐述系统中移动多媒体服务器缓冲区的码率控制和适用于4G网络的RTP协议封包格式的2个衔接作用,可有效解决当前3G网络移动视频信号传输的质量问题。     

节点移动异质性对机会网络性能的影响

机会网络利用节点移动形成的通信机会逐跳传输消息,以"存储-携带-转发"的路由模式实现节点间通信,所以节点的移动对机会网络的通信至关重要。在传统移动模型RWP、RW、RD的基础上建立统一化定义移动模型(UDM),该模型能够刻画以上三种经典模型。在UDM模型下,定义相遇率作为机会网络性能的评价指标,进一步分析节点移动的异质性包括移动速度、移动方向、移动时间及停留时间等属性不同的均值及极差对相遇率的影响,并进行曲线拟合,通过拟合公式,精确分析节点移动异质性对机会网络性能影响的规律性。     

基于频率域多目标MANETs可信路由决策研究

移动Ad-hoc网络(MANETs)具有开放的媒质,动态的拓扑结构,分布式的合作和受限的网络能力等基本特点。网络中移动节点具有匿名性和高度自治的特点,网络通讯依靠在通信路径上的中间节点转发数据包,实现无线传输范围外节点间的正常通信。该文提出了一种独特的MANETs中基于频率下多目标可信路由决策算法,它和现在大多数路由算法都是在时间域下使用单一约束参数选择路由的方式截然不同。利用概率理论分析安全和可信路由,基于概率密度函数的时频相互转化,减小计算复杂度,解决MEANTs中节点间缺乏物理安全以及在低信任水平和节点相互勾结扰乱网络操作情况下,发现可信安全路由难的问题。实例分析证明了此算法的可行性。     

MANETs中基于节点移动度的虚连接的路由

由于移动自组织网络MANETs中节点的快速移动,使得维持源节点与目的节点间的通信路径成为一项挑战性工作。节点的高速移动导致通信链路频繁断裂。为此,提出基于节点移动度的虚连接的路由(MDVRP)。虚路由为一条动态的逻辑路由,其由一系列的特定地理区域构成。每个区域内的节点依据自己的移动度设置转发数据包的定时器,移动度越小,具有优先转发数据包权。MDVRP通过虚路由策略,在源节点与目的节点间建立了多条传输路通,每个节点能独立选取下一跳转发节点,并利用节点移动度,择优选取转发数据包下一跳节点,从而提高链路的稳定性。仿真结果表明,提出的路由协议在端到端传输时延、路由开销以及数据包传输率性能均得到提高。     

基于移动参考节点的无线传感器时钟同步方法

现有对无线传感器网络节点中的时钟同步方法往往通过固定参考节点传递同步信息完成同步。对于固定参考节点通信范围外的节点,需要同步信息在节点间的多跳传输,这造成时间误差的累积以及节点多跳传输的能量损耗,从而影响同步的精度和网络能耗。为解决此问题,提出了基于移动参考节点和最优移动路径的时钟同步方法。首先,采用正六边形的蜂窝覆盖技术选取最优的时钟同步点。其次,结合最优覆盖和选址问题的数学模型,设计最短移动距离的路径。最后,提出了基于MAC层标记多个时间戳实现低能耗单跳同步的机制。与现有方法的实验对比表明,该方法提高了同步时间精度,并降低了通信能耗。     

一种实现机会网络中移动终端屏幕共享的方法

针对传统的屏幕共享环境已不能满足人们的需求等问题,文中利用机会网络可以在间歇式连通环境下实现节点通信的特性,设计并实现了一种基于机会网络的屏幕共享软件。该软件在机会网络的场景下,基于Spring-boot框架,使用FFmpeg视频音频转换器和Node.js跨平台等技术实现移动终端设备在网络间歇性连通状态下的设备搜索、配对、屏幕共享等功能。运行结果表明,在所设定的通信范围内的情况下,该软件能实现基本的数据共享,性能比较稳定。     

移动视频通信的差错控制技术

移动信道是易错、窄带信道,而压缩视频对信道传输差错的影响比较敏感,因此,移动视频通信的差错控制技术成为一个研究热点。该文从信源编码、信道编码方面探讨了移动视频通信的差错控制技术,并用软件实现了H.263+压缩视频在瑞利衰落移动信道上的模拟传输及差错控制,验证移动视频通信差错控制技术的有效性和鲁棒性。     

Cross-layer architecture for scalable video transmission in wireless network

Multimedia applications such as video conference, digital video broadcasting (DVB), and streaming video and audio have been gaining popularity during last years and the trend has been to allocate these services more and more also on mobile users. The demand of quality of service (QoS) for multimedia raises huge challenges on the network design, not only concerning the physical bandwidth but also the protocol design and services. One of the goals for system design is to provide efficient solutions for adaptive multimedia transmission over different access networks in all-IP environment. The joint source and channel coding (JSCC/D) approach has already given promising results in optimizing multimedia transmission. However, in practice, arranging the required control mechanism and delivering the required side information through network and protocol stack have caused problems and quite often the impact of network has been neglected in studies. In this paper we propose efficient cross-layer communication methods and protocol architecture in order to transmit the control information and to optimize the multimedia transmission over wireless and wired IP networks. We also apply this architecture to the more specific case of streaming of scalable video streams. Scalable video coding has been an active research topic recently and it offers simple and flexible solutions for video transmission over heterogeneous networks to heterogeneous terminals. In addition it provides easy adaptation to varying transmission conditions. In this paper we illustrate how scalable video transmission can be improved with efficient use of the proposed cross-layer design, adaptation mechanisms and control information.     

Video transmission in mobile ad hoc networks using multiple interfaces and multiple channels

Mobile Ad hoc NETworks (MANETs) are an important part of wireless communications and the increasing use of mobile devices is confirming that. MANETs can be of great value in Emergency Response situations where communication between mobile deployed units is critical and wired or wireless infrastructures may not be present or functional. In emergency scenarios, multimedia communication is very important for decision making and situation assessment. This requires up‐to‐date (on‐line) information feed on the situation, including voice and video from the affected zone. However, MANETs do not seem to efficiently support multimedia applications, and this is quite evident in video transmission. One way to remedy this is to use more (wireless) interfaces per mobile node and consequently more communication channels. In this work, we perform an analytical study on the use of multiple interfaces and multiple channels (MIMC) in video transmission with respect to the requirements of Emergency Response Ad hoc Networks. More specifically, we examine and present the impact of using MIMC on MANETs during video transmission applications, we evaluate the performance of three basic routing protocols in MANETs, and we propose a channel selection mechanism in MANET nodes with MIMC for enhanced video transmission. In addition, we evaluate video transmission streams with rate adaptation and present comparative results. The proposed mechanism is evaluated using the ns‐2 network simulator and the simulations are performed for a variety of topologies. Simulation results show that the different routing protocols respond differently when MIMC is introduced. The Ad hoc On‐Demand Multipath Distance Vector and (especially) the Ad hoc On‐Demand Distance Vector routing protocols benefit significantly, while the Destination Sequenced Distance Vector shows fewer improvements. The proposed mechanism is shown to be beneficial for transmitting video streams and enhances the network's ability to accommodate more streams and reduce packet delay. Copyright © 2016 John Wiley & Sons, Ltd.     

Adaptive rate controlled,robust video communication over packet wireless networks

Video transmission over wireless packet networks is gaining importance due to the concept of universal personal communication. Further, it is considered an important step towards wireless multimedia. The challenge however is to achieve good video quality over mobile channels, where typically the channel conditions vary due to signal fading. Hence this paper investigates adaptive rate controlled video transmission for robust video communication under packet wireless environment. A combination of mobile and an ATM backbone network is assumed in this work. An error resilient design for the video coder, as proposed in Rajugopal et al. (1996) is employed here. This video coder comprises wavelet transform (WT), multi-resolution motion estimation (MRME) and a robust design for zero tree quantization. Two configurations, one employing MRME and the other using 1D-WT for temporal analysis, are considered for the video coder. Adaptive dynamic rate control is required to adapt the video communication to the channel conditions. It provides more channel protection when the channel is severe and improves the source rate and hence the performance when the conditions are favorable. An algorithm for dynamic rate control under varying channel conditions is proposed in this paper. It is evaluated under narrowband and broadband channel conditions. From the results, it is concluded that the dynamic rate control is very effective in optimizing the quality under varying mobile channel conditions. It was observed that the dynamic rate control provides at least an acceptable video quality under severe channel conditions and a good video quality when the channel conditions are favorable. This revised version was published online in July 2006 with corrections to the Cover Date.     

An Efficient Sport Target Scenes Extracting Methodology for P2P-Based Personal Mobile Beaming Broadcast Service

The prevalence of smartphones surged in recent years, and the expression of personal interest in the heterogeneous devices are being made in the mobile environment. In this paper, we propose an efficient sport target scenes extracting methodology for P2P-based personal mobile beaming broadcasting service, utilizing the smartphone. This application takes advantage of the peer-to-peer communication, anytime, anywhere. Unlike other broadcast applications, we can broadcast sport target scenes in mobile environment considering heterogeneous devices. The proposed method extracts a specific context and displays the context of the target scene from the whole scenes with considering optimal viewer visual sight on devices. We use color-based classification with satisfying viewer visual perception in terms of the number of fast frames within the sport video streaming. Experimental results show that the proposed method is useful to enable an adequate seamless multimedia service for wireless environment.     

Content and Service Protection for the Ubiquitous TV Based on Network Convergence

Today, the ubiquitous multimedia services are becoming more and more popular. However, the secure solutions that confirm the content and service security in these services are still open issues because of various network convergences and device interconnections. This paper investigates an ubiquitous multimedia service architecture and proposes a secure solution for it. In this service architecture, the multimedia content is encoded with scalable video coding and broadcasted via digital video broadcasting for handheld terminals (DVB-H) to mobile terminals, the access right is transmitted by global system for mobile (GSM/GPRS) channel, and the media content and access right can also be transferred from mobile terminals to home TV through WiFi based Wireless Local Area Network. The proposed secure solution supports three kinds of business models by using various content encryption modes and secure transmission protocols. The solution’s security is evaluated and discussed. Since few work has been done to solve this problem, the work proposed in this paper is expected to attract more researchers. Additionally, the solution is also potential for other ubiquitous services.     

Scalable video transcoding for mobile communications

Mobile multimedia contents have been introduced in the market and their demand is growing every day due to the increasing number of mobile devices and the possibility to watch them at any moment in any place. These multimedia contents are delivered over different networks that are visualized in mobile terminals with heterogeneous characteristics. To ensure a continuous high quality it is desirable that this multimedia content can be adapted on-the-fly to the transmission constraints and the characteristics of the mobile devices. In general, video contents are compressed to save storage capacity and to reduce the bandwidth required for its transmission. Therefore, if these compressed video streams were compressed using scalable video coding schemes, they would be able to adapt to those heterogeneous networks and a wide range of terminals. Since the majority of the multimedia contents are compressed using H.264/AVC, they cannot benefit from that scalability. This paper proposes a technique to convert an H.264/AVC bitstream without scalability to a scalable bitstream with temporal scalability as part of a scalable video transcoder for mobile communications. The results show that when our technique is applied, the complexity is reduced by 98 % while maintaining coding efficiency.     

基于网络的视频通信系统的设计

随着移动通信和多媒体通信的飞速发展,构建于无线网络之上的多媒体服务已经被越来越多的用户所接受。2．5代移动通信CDMA的典型带宽为30～50kb／s,可以传输低速的视频,但是对多媒体应用来说,其质量还是未能达到要求。在现有技术条件下,如何在CDMA无线信道中保证视频流的质量以及如何扩大带宽提高视频质量,是值得研究的问题。文中提出了一种在多个CDMA通道中进行视频传输的框架,利用多个CDMA无线信道绑定的方法,提高了视频的帧率和分辨率。     

Intelligent Mobile Video Surveillance System with Multilevel Distillation

This paper proposes a mobile video surveillance system consisting of intelligent video analysis and mobile communication networking. This multilevel distillation approach helps mobile users monitor tremendous surveillance videos on demand through video streaming over mobile communication networks. The intelligent video analysis includes moving object detection/tracking and key frame selection which can browse useful video clips. The communication networking services, comprising video transcoding, multimedia messaging, and mobile video streaming, transmit surveillance information into mobile appliances. Moving object detection is achieved by background subtraction and particle filter tracking. Key frame selection, which aims to deliver an alarm to a mobile client using multimedia messaging service accompanied with an extracted clear frame, is reached by devising a weighted importance criterion considering object clarity and face appearance. Besides, a spatial-domain cascaded transcoder is developed to convert the filtered image sequence of detected objects into the mobile video streaming format. Experimental results show that the system can successfully detect all events of moving objects for a complex surveillance scene, choose very appropriate key frames for users, and transcode the images with a high power signal-to-noise ratio (PSNR).     

基于移动Agent平台的多媒体无线情景仿真

在无线多媒体通信系统中,视频信源在发送端按照一定的编码方式进行编码,形成视频帧,然后在网络层和传输层封装成IP数据包,经过无线信道传输到达接收端,在接收端进行解包和恢复,得到视频帧,再形成重建后的视频流。在此过程中,无线信道的传输特性会影响到视频的传输质量。文中在利用Agent平台的基础上,综合NS2仿真工具,建立研究多媒体信息在无线网络中的传输平台。仿真结果表明,由于无线信道特性的不理想,在接收端恢复视频信息与视频信源相比较,会出现一定的失真     

Long-term rate control for concurrent multipath real-time video transmission in heterogeneous wireless networks

Concurrent multipath transmission provides an effective solution for streaming high-quality mobile videos in heterogeneous wireless networks. Rate control is commonly adopted in multimedia communication systems to fully utilize the available network bandwidth. This paper proposes a novel rate control for concurrent multipath video transmission. The existing rate control algorithms mainly adapt bit rate in the short-term pattern, i.e., without considering the long-term video transmission quality. We propose a long-term rate control scheme that takes into account the status of both the transmission buffer and video frames. First, a mathematical model is developed to formulate the non-convex problem of long-term quality maximization. Second, we develop a dynamic programming solution for online encoding bit rate control based on buffer status. The performance evaluation is conducted in a real test bed over LTE and Wi-Fi networks. Experimental results demonstrate that the proposed long-term rate control scheme achieves appreciable improvements over the short-term rate control schemes in terms of video quality and delay performance.