无线视频传输的RTP/RCU丢包检测

无线网络因为误码丢包导致的错误拥塞使发送端降低发送速率,正确判断网络拥塞状态对网络性能非常重要,实时传输协议的速率控制单元丢包检测方案设置于无线网络和有线网络的边界上,它能够提供网络状况信息给源端,使得源端能够正确的判断网络拥塞状态。仿真实验证明,RTP/RCU的反馈信息可以较好的区分拥塞状况和误码丢包,使得速率控制和差错控制效率得到了较大提高。.     

基于TCP友好速率控制和错误隐藏的H.264视频传输

针对互联网视频传输面临拥塞控制和数据包丢失的问题,使得视频压缩码流在传输过程中经常会遇到因各种原因引起的误码丢包等网络传输错误。结合TCP友好的速率控制算法和H.264的特点,提出了一个集成拥塞控制的端到端视频传输框架,实现了根据网络的变化动态地调整码率和解码端的错误隐藏。实验证明,该视频传输系统框架在不同网络情况下,均可收到较好的效果。     

无线网络中TCP友好流媒体传输改进机制

为保持无线网络中多媒体业务对TCP的友好性，提出了一种适用于无线网络的动态自适应的流媒体传输速率调节机制。该机制通过在接收端区分网络拥塞丢包和链路错误随机丢包，准确判断网络的拥塞状况结合接收端缓存区占用程度，自适应实施多级速率调节，实现了TCP流友好性和流媒体服务质量（QoS）的折中。由于准确区分出无线链路误码丢包和动态调整流媒体QoS要求，该机制能维持较高的网络利用率。仿真实验结果显示在连接数为2和32，链路误码率从0到0．1变化时TCP,TFRC和吞吐量幅度下降幅度较大，WTFCC幅度下降相对较慢，最大相差达2M；在网络负载重时，尽管链路误码率较低，WTFCC区分链路错误与拥塞丢包，因此，端到端丢包率高于TCP和TFRC，但整体传输吞吐量也高于两者。归一化吞吐量显示WTFCC对TCP流友好。     

无线传感器网络拥塞控制机制研究

本论文在分析无线传感器网络不同于普通有线网络的特征后,提出了一种适用于无线传感器网络的TCP 拥塞控制机制DW-TCP,此机制将TCP拥塞窗口分为拥塞丢包窗口和误码丢包窗口,在链路误码率较高时通过降低发送速率提高数据发送的可靠性,节约无线节点的能源消耗和系统不必要的开销,该机制不但考虑到拥塞丢包对数据发送速率的影响,而且考虑到无线链路中的误码丢包对数据发送速率的影响.     

无线网络中传输控制协议的研究

传统TCP(传输控制协议)拥塞控制协议本是为有线网络设计,它假设包丢失完全是由网络拥塞引起。在无线网络环境下除了拥塞丢包外,还存在较高的比特误码率、路由故障等因素引起的丢包现象。当出现非拥塞丢包时,传统TCP将错误地触发拥塞控制,从而引起TCP性能低下。文章在分析传统TCP在无线网络中存在问题的基础上,对目前无线TCP发展和技术进行归纳和比较,进一步给出无线传输协议的研究和发展方向。     

TFRC协议在Ad Hoc网络中的改进及仿真

由于TFRC协议不适合Ad hoc网络环境,这将限制TFRC协议在Ad hoc络中的应用。针对TFRC协议在Ad hoc网络中存在的问题,本文在TFRC算法的基础上提出了一种基于丢包区分机制的TFRC拥塞控制策略,它不仅考虑到了差错误码,切换、连接中断引起的丢包对传输的影响,而且还考虑到了实际的链路本身的差错控制导致的乱序包对算法性能的影响,解决TTFRC算法在Ad hoc网络中因不能正确区分拥塞丢包和误码丢包而造成性能下降的问题,改善TTFRC在Ad hoc网络中的性能。仿真结果表明改进协议的性能优于TFRC。     

用于分级视频流的无线信道顽健传输方案

提出一种针对分级视频流的无线信道传输自适应不等丢包保护方案.在估计当前网络可用带宽及丢包率的基础上,对视频流各层数据进行不等FEC保护及选择适当的传输层数以控制发送速率.为抑制传输误码扩散,提出基本层的FEC包分配算法,利用COP中各帧之间的不同重要性对各基本层数据进行不等丢包保护,使解码端的失真度达到最小.实验结果表明该方案可大大增强分级视频数据的抗误码能力,明显改善视频流媒体的传输质量.     

一种基于H.264的双二叉树GOP差错控制与错误隐藏方法

针对无线应均中的传输错吴和IP网络拥塞导致的视频数据包丢失,H.264采用了一系列的技术.介绍了H.264所使用的差错控制和错误隐藏技术,重点讨论了基于双二叉树GOP(double-binary tree GOP)的差错控制技术.实验结果表明该方案保证了更为有效的抗误码视频码流及良好的修复丢失帧性能.     

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。     

基于无线局域网的实时视频传输与控制

针对无线局域网,研究实现了一种基于RTP/UDP/IP协议的端到端H.263实时视频传输系统.针对无线QoS机制系统应用了一种RTCP反馈友好码率控制算法TFRC,根据丢包率来动态调整发送码率实现拥塞控制.实验表明该传输方案能获得较好的视频传输质量.     

Comparison of video protection methods for wireless networks

An experimental comparison of video protection methods targeted for wireless networks is presented. Basic methods are the data partitioning, reversible variable length coding, and macroblock row interleaving as well as macroblock scattering for packet loss protection. An implementation is described, in which scalable video is protected unequally with forward error correcting codes and retransmissions. Comparisons are performed for simulated wideband code division multiple access channel, and measurements are carried out with wireless local area network, Bluetooth as well as with GSM high speed circuit switched data. For the measurements, point-to-point connections are used. The achieved video quality is examined in our real-time wireless video demonstrator. The performance is measured with peak-signal-to-noise-ratio of received video, data overhead, communication delay, number of lost video frames, and decoding frame rate. Results show that the quality of decoded video can be improved by 1 dB with transparent connections compared to connections designed for general packet data. As a conclusion, a video coding subsystem must have access to the error control in a wireless link for the best quality in varying conditions.     

Rate control for streaming video over wireless

Rate control is an important issue in video streaming applications for both wired and wireless networks. A widely accepted rate control method in wired networks is TCP-friendly rate control (TFRC) (Floyd, 2000). It is equation-based rate control in which the TCP-friendly rate is determined as a function of packet loss rate, round-trip time, and packet size. TFRC assumes that packet loss in wired networks is primarily due to congestion, and as such is not applicable to wireless networks in which the main cause of packet loss is at the physical layer. In this article we review existing approaches to solve this problem. Then we propose multiple TFRC connections as an end-to-end rate control solution for wireless video streaming. We show that this approach not only avoids modifications to the network infrastructure or network protocol, but also results in full utilization of the wireless channel. NS-2 simulations, actual experiments over a 1/spl times/RTT CDMA wireless data network, and video streaming simulations using traces from the actual experiments are carried out to characterize the performance and show the efficiency of our proposed approach.     

Small‐block interleaving for low‐delay cross‐packet forward error correction over burst‐loss channels

By adding the redundant packets into source packet block, cross‐packet forward error correction (FEC) scheme performs error correction across packets and can recover both congestion packet loss and wireless bit errors accordingly. Because cross‐packet FEC typically trades the additional latency to combat burst losses in the wireless channel, this paper presents a FEC enhancement scheme using the small‐block interleaving technique to enhance cross‐packet FEC with the decreased delay and improved good‐put. Specifically, adopting short block size is effective in reducing FEC processing delay, whereas the corresponding effect of lower burst‐error correction capacity can be compensated by deliberately controlling the interleaving degree. The main features include (i) the proposed scheme that operates in the post‐processing manner to be compatible with the existing FEC control schemes and (ii) to maximize the data good‐put in lossy networks; an analytical FEC model is built on the interleaved Gilbert‐Elliott channel to determine the optimal FEC parameters. The simulation results show that the small‐block interleaved FEC scheme significantly improves the video streaming quality in lossy channels for delay‐sensitive video. Copyright © 2013 John Wiley & Sons, Ltd.     

基于H.264 SVC无线视频传输的自适应差错保护方法

提出了一种针对H.264可分级编码(H.264 SVC)的自适应前向纠错编码保护方案.通过比较不同的纠错方案,提出了划分丢包率区间的概念,并根据不同区间的丢包率自适应地选择最佳的纠错方案.仿真结果表明,与单一保护方法相比,所提自适应方法能够取得更好的保护效果,更适于在无线信道中进行视频传输.     

An Adaptive Packet and Block Length Forward Error Correction for Video Streaming Over Wireless Networks

Video streaming over wireless networks is a challenging task due to its high error rate. Forward error correction (FEC) is a popular mechanism to recover lost packets for video streaming. Conventional FEC mechanisms use a whole redundant packet to recover the error source packet, when the packet error occurs with only a few bit errors inside. In this paper, we propose an Adaptive packet and block length FEC (APB-FEC) control mechanism. In order to overcome the high bit error rate, a small packet length reduces the packet error rate and a large FEC block length will enhance the recovery performance. Our proposed APB-FEC can obtain better recovery performance than conventional FEC mechanisms. Hence, APB-FEC can also reduce retransmission overhead. Using extensive emulations, we validate the efficiency of APB-FEC mechanism for video streaming over wireless networks.     

Per-packet rate adaptation for wireless video

Streaming video over error-prone wireless channels is a challenge as the dynamic network conditions and slow adaptation to channel degradations may affect the quality of the streamed video. Unequal error protection (UEP) can potentially address this issue by considering the importance of each video packet and its impact on the quality of reconstructed video. This paper proposes a cross-layer UEP solution for wireless video streaming over IEEE 802.11 networks. Video packets are prioritized based on the relative importance of the video packet. UEP is achieved by adapting the link layer parameters on a per-packet basis, using inherent forward error correction and adaptive modulation capabilities of the 802.11n network. Experimental results revealed that the proposed solution achieves comparable performance to the state-of-the-art methods at a lower complexity.     

Error concealment aware rate shaping for wireless video transport

Streaming of video, which is both source- and channel-coded, over wireless networks faces the challenge of time-varying packet loss rate and fluctuating bandwidth. Rate shaping (RS) has been proposed to reduce the bit-rate of a precoded video bitstream to adapt to the real-time bandwidth variation. In our earlier work, rate shaping was extended to consider not only the bandwidth but also the packet loss rate variations. Rate-distortion optimized rate adaptation is performed on the precoded video that is a scalable coded bitstream protected by forward error correction codes. In this paper, we propose an RS scheme that further takes into account the error concealment (EC) method used at the receiver. We refer to this scheme as EC aware RS (ECARS). When performing ECARS, first ECARS needs to know the benefit/gain of sending each part of the precoded video, as opposed to not sending it but reconstructing it by EC. Then given a certain packet loss probability, the expected gain can be derived and be included in the rate-distortion optimization problem formulation. Finally, ECARS performs rate-distortion optimization to adapt the rate of the precoded video. A two-stage rate-distortion optimization approach is proposed to solve the ECARS rate-distortion optimization problem. In addition to ECARS, the precoding process can be EC aware to prioritize the precoded video based on the gain. We present an example EC aware precoding process by means of macroblock prioritization. Experiment results of ECARS together with EC aware precoding are shown to have excellent performance.     

基于H.264的具有抗分组丢失能力的视频通信系统

针对IP网络环境下实时视频通信的需要，提出了具有抗分组丢失能力的视频通信系统（PRVCS）。系统以H．264编解码算法为核心，在满足实时视频通信要求的同时，将前向分组保护，误码掩盖和交互式防误码扩散三种算法有机结合，在丢包环境下保证恢复视频的主客观质量。其中重点研究了PRVCS所使用的算法、体系结构以及系统的具体实现。     

A retransmission‐based scheme for video streaming over wireless channels

Efficient resource allocation is a key factor to improve the efficiency of video transmission over wireless channels. To increase the number of correctly received video frames at the decoder, it is desirable to reduce the video source rate while increasing error protection when the wireless channel is anticipated to be bad or when the receiver buffer is approaching starvation. In this study, we introduce a retransmission‐based adaptive source‐channel rate control scheme for video transmission over wireless packet networks. In this scheme, the level of adaptiveness is optimized to reduce the bandwidth requirement while guaranteeing delay and loss bounds. The proposed scheme has the advantage of providing closed‐form expressions of the near‐optimum parameters of the proposed model, which are then fed back to the transmitter to scale both the source and channel rates adaptively. Simulation and numerical investigations are carried out to verify the adequacy of the analysis and study the impact of the adaptive process on the continuity of the video playback process. Copyright © 2009 John Wiley & Sons, Ltd.     

TCP-friendly flow control of wireless multimedia using ECN marking

In a wireless network packet losses can be caused not only by network congestion but also by unreliable error-prone wireless links. Therefore, flow control schemes which use packet loss as a congestion measure cannot be directly applicable to a wireless network because there is no way to distinguish congestion losses from wireless losses. In this paper, we extend the so-called TCP-friendly flow control scheme, which was originally developed for the flow control of multimedia flows in a wired IP network environment, to a wireless environment. The main idea behind our scheme is that by using explicit congestion notification (ECN) marking in conjunction with random early detection (RED) queue management scheme intelligently, it is possible that not only the degree of network congestion is notified to multimedia sources explicitly in the form of ECN-marked packet probability but also wireless losses are hidden from multimedia sources. We calculate TCP-friendly rate based on ECN-marked packet probability instead of packet loss probability, thereby effectively eliminating the effect of wireless losses in flow control and thus preventing throughput degradation of multimedia flows travelling through wireless links. In addition, we refine the well-known TCP throughput model which establishes TCP-friendliness of multimedia flows in a way that the refined model provides more accurate throughput estimate of a TCP flow particularly when the number of TCP flows sharing a bottleneck link increases. Through extensive simulations, we show that the proposed scheme indeed improves the quality of the delivered video significantly while maintaining TCP-friendliness in a wireless environment for the case of wireless MPEG-4 video.