End-to-End QoS for Video Delivery Over Wireless Internet

Providing end-to-end quality of service (QoS) support is essential for video delivery over the next-generation wireless Internet. We address several key elements in the end-to-end QoS support, including scalable video representation, network-aware end system, and network QoS provisioning. There are generally two approaches in QoS support: the network-centric and the end-system centric solutions. The fundamental problem in a network-centric solution is how to map QoS criterion at different layers respectively, and optimize total quality across these layers. We first present the general framework of a cross-layer network-centric solution, and then describe the recent advances in network modeling, QoS mapping, and QoS adaptation. The key targets in end-system centric approach are network adaptation and media adaptation. We present a general framework of the end-system centric solution and investigate the recent developments. Specifically, for network adaptation, we review the available bandwidth estimation and efficient video transport protocol; for media adaptation , we describe the advances in error control, power control, and corresponding bit allocation. Finally, we highlight several advanced research directions.     

MR2_ODMRP: Improvement of End-to-End Transmission Delay in Wireless Multicast Routing

With recent advances in wireless technology, the importance of the capability to use multiple transmission rates and multiple radios has been widely recognized. In this paper, multi-rate and multi-radio (MR2) characteristics are exploited to improve end-to-end transmission delay for reliable multicasts. To achieve this goal, maximum potential rate based on multiple rates and radio based transmission delay with a different number of available radios are investigated in the construction of multicast routes. Multi-rate multi-radio on-demand multicast routing protocol (MR2_ODMRP), a protocol that makes ODMRP suitable for a MR2 environment, is proposed. An integer linear programming model is proposed to obtain the optimal tree as well as the rate and radios at each node of the tree for each multicast service. The solution is employed to evaluate the performance of the MR2_ODMRP. From the simulation, it is shown that the MR2_ODMRP produces nearly optimal solutions even in environments with a large number of nodes. It outperforms the ODMRP in wireless mesh networks. The end-to-end transmission delay is improved by a factor of four compared to the ODMRP.     

恶劣信道下无线ATM信元传输性能分析

本文对无线ATM中的信元传输问题进行了研究．文中提出一种新的信元格式，对信元的检错和纠错方式以及信元定界过程中的校核次数与保护次数等参数进行了修改以适应新的环境．文中从理论上分析了各个参数对信元同步性能的影响，并对不同误码率情况下的信元同步性能进行了计算，给出了详细的结果．     

基于信道接入的通信端到端传输时延分析

文中利用信道接入技术对通信端到端的传输时延进行计算,首先将时延分为传输设备传输时延、数据帧长度时延、线路时延,然后计算通信端到端的传输时延,以获得整个通信信号时序序列的计算方法。利用信道接入技术,采用计算模型,计算时延序列中单组信号的出现概率,在此基础上计算出通信端到端的传输时延。最后开展仿真实验,实验结果表明信道接入能够减少计算误差。     

基于多手段融合的便携式无线视频传输系统

针对利用3G网络传输实时视频存在的问题,提出一种基于超短波通信和3G网络的便携式无线视频传输系统,介绍了系统的组成结构和工作原理,着重阐述了多链路聚合和超短波通信等关键技术.该系统拓展了移动通信网络的应用范围,提高了无线视频传输系统的灵活性和稳定性,具有广泛的应用前景.     

无线网络中视频传输的信道失真分析

无线网络中进行视频传输,信道误码会造成数据包的丢失,引起图像的失真,即信道失真.本文对无线信道进行分析并给出一种信道失真模型.这种信道失真模型估计准确,计算复杂度低,适合于无线视频的应用.     

Optimizing the End-to-End Performance of Reliable Flows over Wireless Links

Pure end-to-end error recovery fails as a general solution to optimize throughput when wireless links form parts of the end-to-end path. It can lead to decreased end-to-end throughput, an unfair load on best-effort networks, and a waste of valuable radio resources. Link layer error recovery over wireless links is essential for reliable flows to avoid these problems. We demonstrate this through an analysis of a large set of block erasure traces measured in different real-world radio environments, with both stationary and mobile hosts. Our analysis is based on a case study of the circuit-switched data service implemented in GSM. We show that the throughput on this wireless channel can be increased by using a larger (fixed) frame size for the reliable link layer protocol. This yields an improvement of up to 25% when the channel quality is good and 18% even under poor radio conditions. Our results suggest that adaptive frame length control could further increase the channel throughput. Finally, we discuss link and transport layer error control mechanisms and their interactions with end-to-end congestion control schemes. For reliable flows, we argue in favor of highly persistent error recovery and lossless handover schemes implemented at the link layer.     

一种无线视频传输系统的实现

提出了一种基于H．261标准和蓝牙标准的视频压缩算法的无线传输系统。系统以自主研制开发的H.261标准的视频编、解码板为平台，通过蓝牙进行无线视频数据传输，在编解码板和蓝牙模块之间采用了简单方便而且技术相对成熟的高速UART，并采用FPGA来实现，能通过软件实现对数据码流的控制。因此，系统很好地实现了视频数据压缩算法和传输方式的可升级性。实际应用表明，该系统取得了良好视频效果，具有很好的应用前景。     

无线视频传输系统的设计

给出了一种无线视频传输系统的设计方法.发送部分的设计是基于TI开放式多媒体应用平台(OMAP),接收部分由普通PC控制.将采集到的图像数据按MPEG-4或MJPEG标准进行编码,得到的码流通过蓝牙进行传输.对于MPEG-4码流,帧率可以达到30 f/s,传输距离可以达到100 m.对于MJPEG码流,可以得到高质量的图片.当接收部分只接收数据而不进行解码时,80 m内的稳定的传输速率可达到1.1 Mb/s.     

无线宽带网络中的视频同传应用

本文首先对当前的视频同传技术和无线宽带技术进行了分析;然后分别针对无线宽带中的视频QoS保障,视频质量提高这两个技术难点进行了讨论;最后给出了青岛帆船赛视频同传项目实例。通过这一无线宽带网络中进行视频同传的实例,可以看出,本文提出的解决方案能够克服现有问题,将无线宽带网络和视频同传良好的结合在一起。     

基于H.261标准的无线视频传输系统的实现

提出并实现了一种基于H.261标准视频压缩算法的蓝牙无线传输系统.系统以作者自主研发的基于H.261标准的视频编解码板为平台,通过蓝牙进行短距离的无线视频数据传输,系统能通过软件对视频数据码流的控制,很好地实现视频数据压缩算法和传输方式的升级.实际应用表明,该系统取得了良好的视频效果,具有很好的应用前景.     

COFDM技术在无线视频传输中的应用

编码正交频分复用（Coded orthogonal frequency division multiplexing, COFDM）是一种多载波数字通信调制技术,它具有频谱利用率高和可对抗多径时延扩展等特点。文章介绍了COFDM技术的基本原理,对基于该技术的无线视频传输系统在海上视频传输的实际应用进行了分析论述。     

Partially Overlapped Channels- and Flow-Based End-to-End Channel Assignment for Multi-Radio Multi-Channel Wireless Mesh Networks

Capacity reduction is a major problem faced by wireless mesh networks. An efficient way to alleviate this problem is proper channel assignment. Current end-toend channel assignment schemes usually focus on the case where channels in distinct frequency bands are assigned to mesh access and backbone, but actually backbone network and access network can use the same IEEE 802.11 technology. Besides, these channel assignment schemes only utilize orthogonal channels to perform channel assignment, and the resulting network interference dramatically degrades network performance. Moreover, Internet-oriented traffic is considered only, and peerto-peer traffic is omitted, or vice versa. The traffic type does not match the practical network. In this paper, we explore how to exploit partially overlapped channels to perform endto-end channel assignment in order to achieve effective end-to-end flow transmissions. The proposed flow-based end-to-end channel assignment schemes can conquer the limitations aforementioned. Simulations reveal that loadaware channel assignment can be applied to networks with stable traffic load, and it can achieve near-optimal performance; Traffic-irrelevant channel assignment is suitable for networks with frequent change of traffic load,and it can achieve good balance between performance and overhead. Also, partially overlapped channels’ capability of improving network performance is situation-dependent, they should be used carefully.     

无线视频传输的容错编码研究

基于无线视频监控传输技术进行无线信道视频图像传输的过程中,经常面临数据传输错误、带宽变化、网络拥塞导致的视频数据丢失问题,严重影响了图像质量。Joint Video Team(JVT)of ISO/IECMPEG and ITU-T VCEG提出了可伸缩视频编码(SVC),可实现视频空间、时间和图像质量的完全伸缩,本文结合率失真优化算法将可伸缩编码作为容错工具,引入了不同层数据,根据B-D代价函数决定自动重传机制,降低了视频数据丢失对图像质量的影响。仿真结果表明,该方法大大提高了视频码流的抗误码能力和传输的鲁棒性。     

Cross-Layer Optimization for Video Summary Transmission over Wireless Networks

Video summarization has gained increased popularity in the emerging multimedia communication applications, however, very limited work has been conducted to address the transmission problem of video summary frames. In this paper, we propose a cross-layer optimization framework for delivering video summaries over wireless networks. Within a rate-distortion theoretical framework, the source coding, allowable retransmission, and adaptive modulation and coding have been jointly optimized, which reflects the joint selection of parameters at physical, data link and application layers. The goal is to achieve the best video quality and content coverage of the received summary frames and to meet the delay constraint. The problem is solved using Lagirangian relaxation and dynamic programming. Experimental results indicate the effectiveness and efficiency of the proposed optimization framework, especially when the delay budget imposed by the upper layer applications is small, where more than 10% distortion gain can be achieved.     

联合译码在图像无线传输中的应用

对Turbo码编码结构作了适当调整,进行信道编码的不仅有信源编码信息还有信源信息的统计特性,将信源编码后码流中存在的残留冗余特性应用到被传输的信源编码信息在进行Turbo码译码的算法中,给出了实验结果。通过结果比较发现,改进算法提高了Turbo码译码的纠错性能。     

无线信道图像传输系统设计

针对某红外图像在干扰信道中的可靠传输问题,通过分析系统使用特点：处于干扰信道环境,要求图像传输实时性好、高保真显示及容量大,采用了多频点传输,带限信道,合适的天线形式和信源信道联合编解码解决的方案,解决了干扰信道下的图像数据可靠传输问题,应用大规模FGPA完成信号处理的工程实现,通过试验验证了系统满足传输距离及时延要求。     

MPEG-4 Video Transmission over Wireless Networks: A Link Level Performance Study

With the scalability and flexibility of the MPEG-4 and the emergence of the broadband wireless network, wireless multimedia services are foreseen to become deployed in the near future. Transporting MPEG-4 video over the broadband wireless network is expected to be an important component of many emerging multimedia applications. One of the critical issues for multimedia applications is to ensure that the quality-of-service (QoS) requirement to be maintained at an acceptable level. This is further challenged in that such a service guarantee must be achieved under unreliable and time-varying wireless channels. In this paper we study the link level performance of MPEG-4 video transmission over the uplink of an unreliable wireless channel. We introduce the discrete time batch Markovian arrival process (DBMAP) with two types of arrivals to model the MPEG-4 video source, which takes into account the inherent nature of the adaptiveness of the video traffic. We prove that in a hidden Markov modeled (HMM) wireless channel with probabilistic transmission, the service time for an arbitrary radio link control (RLC) burst follows phase type (PH-type) distribution. We show that the link level performance of a wireless video transmission system can be modeled by a DBMAP/PH/1 priority queue, and present computation algorithm and numerical results for the queueing model. Extensive simulations are carried out on the queueing behavior of the video transmission buffer, as well as on the packet level error behavior of the video data. The results demonstrate that video quality can be substantially improved by preserving the high priority video data during the transmission.     

Energy-Efficient Video Transmission Over a Wireless Link

Energy minimization is an important design goal in wireless video transmission. We examine how the RF energy and the analog circuit energy, which account for a large part of the energy consumption for wireless video transmission, can be controlled with physical-layer parameters (e.g., modulation level, bit rate, bit error rate, and multiple access interference) and link-layer specifications (e.g., the buffer status, idle time, and active time). Building on these insights, we develop three energy-efficient video transmission schemes for the single-user system, i.e., frame-by-frame transmission, group of pictures (GOP)-by-GOP transmission, and client-buffer-related energy-efficient video transmission (CBEVT). Our simulations indicate that energy savings of up to 85% is achievable in the radio frequency (RF) front end using the CBEVT algorithm. We also present an energy-efficient optimal smoothing algorithm for reducing the RF front-end energy consumption and the peak data rate. For CDMA-based multiuser systems, we propose an RF front-end energy model that assumes perfect power control. We find the signal-to-interference-noise ratio (SINR) for the entire system that minimizes the total energy consumption. We propose the multiuser-based energy-efficient video transmission (MBEVT) algorithm, which can achieve energy savings of up to 38% for a six-user CDMA system with an independent 16-MB buffer for every uplink.      

无线通讯技术与视频传输

近年来,无线通讯技术的快速发展、移动数据传输速率的大幅提升推动了视频、社交等应用以移动互联网为载体的大发展.以WiFi (Wireless Fidelity,无线局域网技术)为代表的近距离无线通讯技术和以LTE (Long TermEvolution,长期演进技术)为代表的广域蜂窝无线通讯技术,以更高的带宽和更低的成本向用户提供了更为丰富、便捷的无线应用体验.本文对现阶段无线通讯技术的发展概况进行分类介绍,并分析几种主流无线通讯标准的技术特点以及对于视频传输业务的支持情况.