基于H.264率失真模型的无线信源信道联合编码方案

针对H.264编码器的率失真特性,建立了一种新的H.264编码率失真(R-D,rate-distortion)模型:然后基于该R-D模型和Turbo码的抗差错特性,对无线环境下的端到端视频传输失真进行了深入的分析,提出了一种无线信道下的自适应视频信源信道联合编码(JSCC,joint source channel coding)方案,该方案可以自适应地根据当前无线信道的具体状况,将网络可用带宽在信道编码和信源编码之间进行最优的分配,使得端到端的传输失真达到最小.实验结果表明,与固定选择信道编码速率方案相比,该方案可以显著提高传输的可靠性,在接收端可以获得更好的视频重建质量.     

无线视频通讯中的自适应差错非均匀保护方案

针对划分了重要级别的H-264视频编码数据提出五种可能的不平等保护策略，通过测试和比较，最终提出一种高误码率下无线视频可靠性传输的全局最优不平等保护策略。仿真实验表明，在无线网络带宽和信道误码率不同的情况下，这种最优策略都能使接收端信源解码后的视频图像峰值信噪比(PSNR)既稳定又具鲁棒性。     

基于视频代理和不对等重传的视频抗差错方法

针对无线视频传输应用,提出了一种基于视频代理的不对等重传方法.该方法考虑了CoP中视频帧的不均等重要性和无线信道的时交突发错误特性,尝试将突发错误转移至相对不重要的视频帧中.视频代理感知信道条件的变化,从而自适应地为不同视频帧分配不同的重传策略.实验结果证明了该方法的有效性.     

基于H.324/M协议的视频差错控制研究

随着无线技术的发展以及市场的需要,无线视频通讯必将得到广泛应用。为研究信道误码对压缩视频质量的影响,以及评估视频编码的差错恢复性能,本文构建了基于ITU-T无线终端协议H.324/M的仿真平台,并利用此平台对MPEG4视频进行一种简单的非均衡保护传输仿真。     

基于跨层码率适配和差错控制的3D视频无线传输方法

针对纹理视频加深度序列的3D视频无线传输,本文提出一种基于跨层优化的码率适配和差错控制方法.通过最小化端到端3D视频失真,均衡调整和配置应用层3D视频编码的码率和帧内编码更新比例,以及物理层的调制和编码模式,达到信源码率适配信道带宽以及应用层差错控制和物理层信道保护强度相互平衡的目的,进而提高接收端的3D虚拟视点视频质量.实验结果表明,提出的方法能有效的提高3D视频无线传输的性能.     

一种基于信道预测的FGS视频信源信道联合编码新方法

提出一种基于信道预测的无线FGS视频信源信道联合编码的新方法。该方法利用马尔可夫链对无线信道进行预测，针对FGS分级编码视频流的优先级差异，提供非均匀FEC信道编码保护，根据信道预测的结果，调整视频传输的时隙位置，优化信道编码效率，使得视频在无线传输过程中所需要的数据量最小，同时满足用户的失真要求。实验结果证明了该方法的有效性。     

基于功率分配的H.264空时编码方案

针对传统视频传输重建图像质量低的问题,提出了一种H.264码流传输的新方案。在信源端,根据H.264码流重要性差异,将其分为两部分。采用MIMO信道传输视频信号,在保持总发射功率恒定的情况下,在两根天线上动态分配发射功率。仿真结果表明,在同等信道条件下,提出的方案有效提高了接收端的重建图像质量。     

一种用于H.264视频容错转码的帧内宏块刷新算法

无线网络信道具有误码率高、延时抖动等不稳定的特性。为了保证视频信息从有线网络到无线网络中传输的质量,需要对视频进行容错转码。基于H.264容错转码系统,利用转码结构中解码部分的运动矢量信息,自适应地在编码部分进行帧内刷新,以提高视频的抗误码能力。实验结果对比表明,该帧内刷新算法能够以较少的比特率为代价,有效地提高了接收端的视频质量。     

小波编码图像联合信源信道解码算法的研究

为提高图像在噪声信道中传输的可靠性,该文提出了一种图像联合信源信道解码方案。信源图像首先经离散小波变换,压缩编码。编码数据经RCPC(率兼容删余卷积码)信道编码保护,通过噪声信道传输。在接收端的改进的APRI-SOVA (先验信息软输出维特比算法)在信道解码时,不仅利用了信道输出的软判决,而且进一步利用了信源解码器提供的当前解码的比特的可靠性信息。仿真结果显示,有效利用信源数据中遗留的相关性,能够实现图像解码质量的提高。     

水下无线光通信动态阈值判决技术研究与性能分析

针对海洋湍流信道环境下固定阈值判决方案导致水下无线光通信系统性能恶化的问题,提出了一种动态阈值判决方案。该方案基于水下湍流信道慢衰落的特性,在发送端将数据以帧为单位进行发送,接收端则根据接收帧前导码的幅度每帧更新一次判决阈值。采用蒙特卡洛法和Gamma-Gamma信道模型对水下无线光通信系统进行仿真,仿真结果表明：在弱湍流信道环境下,当系统误码率为10^-6时,动态阈值判决方案比固定阈值判决方案的误码性能提升5.4 dB;在中、强湍流信道环境下,动态阈值判决方案能够有效抑制误码率门限现象的产生。     

Power Efficient Video Multipath Transmission over Wireless Multimedia Sensor Networks

This paper proposes a power efficient multipath video packet scheduling scheme for minimum video distortion transmission (optimised Video QoS) over wireless multimedia sensor networks. The transmission of video packets over multiple paths in a wireless sensor network improves the aggregate data rate of the network and minimizes the traffic load handled by each node. However, due to the lossy behavior of the wireless channel the aggregate transmission rate cannot always support the requested video source data rate. In such cases a packet scheduling algorithm is applied that can selectively drop combinations of video packets prior to transmission to adapt the source requirements to the channel capacity. The scheduling algorithm selects the less important video packets to drop using a recursive distortion prediction model. This model predicts accurately the resulting video distortion in case of isolated errors, burst of errors and errors separated by a lag. Two scheduling algorithms are proposed in this paper. The Baseline scheme is a simplified scheduler that can only decide upon which packet can be dropped prior to transmission based on the packet’s impact on the video distortion. This algorithm is compared against the Power aware packet scheduling that is an extension of the Baseline capable of estimating the power that will be consumed by each node in every available path depending on its traffic load, during the transmission. The proposed Power aware packet scheduling is able to identify the available paths connecting the video source to the receiver and schedule the packet transmission among the selected paths according to the perceived video QoS (Peak Signal to Noise Ratio—PSNR) and the energy efficiency of the participating wireless video sensor nodes, by dropping packets if necessary based on the distortion prediction model. The simulation results indicate that the proposed Power aware video packet scheduling can achieve energy efficiency in the wireless multimedia sensor network by minimizing the power dissipation across all nodes, while the perceived video quality is kept to very high levels even at extreme network conditions (many sensor nodes dropped due to power consumption and high background noise in the channel).     

Joint source-channel coding and power adaptation for energy efficient wireless video communications

We consider efficiently transmitting video over a hybrid wireless/wire-line network by optimally allocating resources across multiple protocol layers. Specifically, we present a framework of joint source-channel coding and power adaptation, where error resilient source coding, channel coding, and transmission power adaptation are jointly designed to optimize video quality given constraints on the total transmission energy and delay for each video frame. In particular, we consider the combination of two types of channel coding—inter-packet coding (at the transport layer) to provide protection against packet dropping in the wire-line network and intra-packet coding (at the link layer) to provide protection against bit errors in the wireless link. In both cases, we allow the coding rate to be adaptive to provide unequal error protection at both the packet and frame level. In addition to both types of channel coding, we also compensate for channel errors by adapting the transmission power used to send each packet. An efficient algorithm based on Lagrangian relaxation and the method of alternating variables is proposed to solve the resulting optimization problem. Simulation results are shown to illustrate the advantages of joint optimization across multiple layers.     

基于USRP的网络编码视频传输研究与设计

物理层网络编码理论及其应用是当前通信网络领域研究的热点,但是真实场景下的实验平台建设还很少见.文通过USRP＋PC软件无线电平台在无线双向中继网络场景下,实现了物理层网络编码视频传榆的功能.仿真结果表明,应用网络编码的视频传输和传统的方式相比,可以有效地提高视频的传输质量和效率.     

一种无线视频传输的跨层自适应不平等保护方法

无线网络的异构性给多媒体业务带来了很大的挑战,跨层设计因此成为研究的热点。该文提出一种针对视频传输的跨层自适应保护方法,根据信道变化自适应选择应用层、链路层和物理层最优的编码和传输策略组合,对视频码流中具有不同重要性的数据进行不平等保护。仿真结果证明,该文提出的跨层保护方法能够在信道条件比较差的情况下提供更好的视频传输质量。     

Robust channel estimation for the OFDM-based WLAN systems with imperfect synchronization

As an effective technique for combating multipath fading and for high data rate transmission over wireless channels, orthogonal frequ- ency division multiplexing (OFDM) is extensively used in wireless local area network (WLAN) systems to support high-performance bandwidth- efficient multimedia services. In this paper, a robust channel estimation scheme is proposed for the OFDM-based WLAN systems with imperfect synchronization. The frame structure information, the preamble information, the pilot information are efficiently utilized in the proposed channel estimation scheme. Simulation results are used to illustrate the performance of the proposed scheme.     

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.     

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。     

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.     

Scalable video coding and transport over broadband wirelessnetworks

With the emergence of broadband wireless networks and increasing demand of multimedia information on the Internet, wireless multimedia services are foreseen to become widely deployed in the next decade. Real-time video transmission typically has requirements on quality of service (QoS). However, wireless channels are unreliable and the channel bandwidth varies with time, which may cause severe degradation in video quality. In addition, for video multicast, the heterogeneity of receivers makes it difficult to achieve efficiency and flexibility. To address these issues, three techniques, namely, scalable video coding, network-aware adaptation of end systems, and adaptive QoS support from networks, have been developed. This paper unifies the three techniques and presents an adaptive framework, which specifically addresses video transport over wireless networks. The adaptive framework consists of three basic components: (1) scalable video representations; (2) network-aware end systems; and (3) adaptive services. Under this framework, as wireless channel conditions change, mobile terminals and network elements can scale the video streams and transport the scaled video streams to receivers with a smooth change of perceptual quality. The key advantages of the adaptive framework are: (1) perceptual quality is changed gracefully during periods of QoS fluctuations and hand-offs; and (2) the resources are shared in a fair manner     

Dynamic Resource Allocation for Scalable H.264/AVC Video Transmission over MIMO Wireless Systems

In this study, a channel selection algorithm is proposed to enhance the transmission rate for scalable video coding (SVC) source transmission over multi-input multi-output (MIMO) wireless systems. The proposed algorithm allows each layer of SVC video to choose its appropriate channel in wireless MIMO systems based on channel state information for transmission rate enhancement. Here, this difficult problem is converted into mathematical optimization problem to improve the performance of SVC video transmission. Experimental results show that the transmission rate of the proposed method outperforms the existing scheme.