802.11g无线局域网视频性能评价的仿真研究

无线局域网的发展和视频编解码技术的进步,让两者结合越来越紧密.但视频传输需要大量带宽确保,对时延有严格要求,让无线局域网的视频性能成为目前的一个研究重点.对网络视频性能的多种影响因素进行分析,结合无线局域网和主流视频编解码的特点,提出改进的802.11g无线局域网视频性能评价模型和基于视频业务的自适应的前向纠错算法,得到了H.264编解码条件下的视频性能结果,对前向纠错算法对视频性能的影响进行分析.     

基于无线局域网的视频传输系统的研究和实现

实现局域网视频传输是Internet视频通信的基础。该文从无线局域网用户的角度出发,研究和实现基于无线局域网的视频传输系统。所涉及技术包括无线局域网的组织、多线程编程和套接字网络编程等。     

基于IEEE 802.11无线局域网的视频流接入控制

从理论上分析了基于IEEE802.11b无线局域网的UDP可用带宽,重点分析了视频码流数目N、视频帧率与视频帧的平均帧长度间的关系,给出了分析结果。在此基础上,说明了无线局域网上视频流接入控制机制的必要性。实验结果表明,其结果很好地反映了802.11无线局域网上视频码流传输的实际特性,为实现基于IEEE802.11无线局域网的视频流接入控制提供了依据。     

多点对点无线视频图像传输系统的研究和实现

视频通信是目前计算机和通信领域的一个热点。随着计算机技术、网络通信和多媒体技术 ,特别是视频压缩技术的发展 ,视频传输将成为IP网络的重要业务。近些年来 ,随着局域网的应用领域不断拓宽和现代通信方式的不断变化 ,尤其是移动和便携式通信的发展 ,无线局域网 (WLAN)也逐渐成为计算机通信领域的一个热点。论述了应用无线局域网进行多点对点传输视频的特点 ,并提出一种采用多线程 (Multi thread)和套接口 (Socket)技术实现多点对点无线视频传输系统的解决方案     

无线局城网的网络安全方案改进措施探讨

无线接入网技术是当前国际上的研究热点,无线局域网作为一种无线接入技术得到了迅速的发展,但是随后一系列的研究表明,早期的无线局域网安全机制存在很大的安全隐患。随着无线局域网的不断普及,无线局域网的安全成为了制约无线局域网应用拓展的重要因素之一。因此对无线局域网安全问题的研究有着重要的意义。本文从无线局域网的安全威胁、无线局域网网络结构、无线局域网安全业务和无线局域网安全方案改进措施四方面进行阐述。     

无线局域网网络安全措施的改进研究

无线接入网技术是当前国际上的研究热点,无线局域网作为一种无线接入技术得到了迅速的发展,但是随后一系列的研究表明,早期的无线局域网安全机制存在很大的安全隐患。随着无线局域网的不断普及,无线局域网的安全成为了制约无线局域网应用拓展的重要因素之一。本文从无线局域网的安全威胁、无线局域网网络结构、无线局域网安全业务和无线局域网安全方案改进措施四方面进行阐述。     

基于云台的视频无线传输系统设计

随着自动化、通信、物联网和图像处理等技术的迅速发展,基于嵌入式的视频无线传输技术越来越趋于成熟。本文根据视频传输的实际需求,将无线局域网技术、嵌入式技术和视频传输技术有机地结合在一起,设计并实现了一种高可靠性、运用便捷的基于云台控制的视频无线传输系统。本设计从系统的研究背景、国内外研究现状及发展方向和本次设计题目的研究意义等几个方面进行简要介绍,并对云台控制电路的软硬件设计及实时视频传输的软件实现进行详细的论述。通过对软硬件的设计和优化,系统真正地实现了视频在局域网内的实时传输,可通过手机浏览网页的方式查看实时的动态视频画面,达到最初设计要求。     

基于ARM11的嵌入式无线视频终端的设计

随着无线局域网的广泛应用,为了在嵌入式系统中整合无线局域网宽带通信技术进行视频传输;提出一种基于ARM11硬件平台和嵌入式Linux操作系统的无线视频终端系统的设计方案,给出系统的总体设计和主要功能模块的实现,其中包括视频采集模块、无线视频传输模块的硬件设计,嵌入式Linux的驱动程序移植、H.264数字视频压缩及应用程序实现等;该系统实现了802.11无线局域网内的视频传输,实时监测网络的数据流量和拥塞状况,提高网络传输质量,保证视频播放流畅性,可靠性高且易于使用;实践证明本系统稳定性高,实时性好,运行可靠,可应用于视频监控领域。     

无线局域网的安全性研究

无线局域网因为其移动性、投资少、可扩展性好等优点而得到了广泛的使用．但是由于其本身的特性．无线局域网比有线网络更容易受到攻击，其安全问题更加突出。基于此，本文主要对无线局域网的安全性进行研究：首先简单介绍了无线局域网的特点，然后对无线局域网面临的安全威胁进行了深入分析，总结了其面临的两个方面的安全问题，最后对相应的安全措施进行了分析与研究。     

浅谈无线局域网技术

文章介绍了无线局域网的优势及特点,从Bluetooth、IEEE802.11X、HiperLAN2、LMDS、MMDS等无线局域网规范介绍了无线局域网标准,介绍了无线局域网结构,并对无线局域网的组网问题进行了讨论,对无线局域网的应用进行了阐述.     

量化因子在IEEE 802. 11 b/e无线局域网视频流传输中的图像质量性能仿真研究

在NS2-MyEvalvid模型基础上分析了量化因子对传输图像质量性能的影响,并在NS2平台上通过仿真实现了基于Evalvid机制的视频流在无线局域网环境下的传输,总结归纳了编码相关参数仿真视频流在无线网络图像传输过程中的一般方法,通过改变编码的量化因子,得到了在多速率无线局域网环境(802.11b/e)下视频流传输的图像平均延迟和平均PSNR值.分析表明,802.11e在视频流传输性能上比802.11b具有更好的表现.     

一种适合实时视频传输的混合ARQ加条件跳帧算法研究

论文讨论视频数据在无线局域网(WLAN)中的实时传输问题。采用IEEE802.11b协议,WLAN可提供高达11Mbps的传输速率,在没有干扰和没有拥塞的情况下,其环境完全满足实时视频传输的需要。但在干扰和拥塞严重的情况下,视频帧的延时很大,无法满足实时播放的要求。文献犤1犦提出了一种混合ARQ算法,可较好地解决视频帧的传输延迟问题,但在网络负载很重时,丢包率很高,视频序列的重构质量很差。因而在深入研究IEEE802.11b协议的核心MAC层的基础上,参考文献犤1犦,提出了一种新的适合实时视频传输的混合ARQ算法,结合高层的基于反馈信息的条件跳帧技术,可很好地解决视频帧的延时问题,同时传输的可靠性也很高。     

Video Capacity of WLANs With a Multiuser Perceptual Quality Constraint

As wireless local area networks (WLANs) become a part of our network infrastructure, it is critical that we understand both the performance provided to the end users and the capacity of these WLANs in terms of the number of supported flows (calls). Since it is clear that video traffic, as well as voice and data, will be carried by these networks, it is particularly important that we investigate these issues for packetized video. In this paper, we investigate the video user capacity of wireless networks subject to a multiuser perceptual quality constraint. As a particular example, we study the transmission of AVC/H.264 coded video streams over an IEEE 802.11a WLAN subject to a constraint on the quality of the delivered video experienced by r% (75%, for example) of the users of the WLAN. This work appears to be the first such effort to address this difficult but important problem. Furthermore, the methodology employed is perfectly general and can be used for different networks, video codecs, transmission channels, protocols, and perceptual quality measures.      

Delay-Constrained and R-D Optimized Transrating for High-Definition Video Streaming Over WLANs

In this study, we propose bit-rate adaptation techniques for compressed high-definition video transmission over wireless home networks. Application-layer methods are developed to minimize quality impairments caused by wireless channel degradations. A transrater located at a home video server adjusts the transmission rate of the video stream based on bandwidth measurements. We consider delay constraints of multiple video frames across various time scales, and dynamically select an appropriate time scale for bit-rate adjustments. This novel feature prevents playout buffer underflows and avoids unnecessary rate reductions. Furthermore, distortion due to transrating is minimized by coding type-dependent rate allocation among the frames to be transmitted in the projected time scale. Using a realistic simulation setup, we demonstrated that the proposed technique significantly reduces video glitches. Up to 3.12 dB average PSNR improvement is achieved, compared to a non-delay constrained rate adaptation method, which also utilizes bandwidth measurements. Our approach maintains compliance with existing wireless local area (WLAN) devices and standards, as well as consumer video standards and applications.      

Wireless multimedia delivery over 802.11e with cross-layer optimization techniques

The use of wireless networks has spread further than simple data transfer to delay sensitive and loss tolerant multimedia applications. Over the past few years, wireless multimedia transmission across Wireless Local area Networks (WLANs) has gained a lot of attention because of the introduction of technologies such as Bluetooth, IEEE 802.11, 3G, and WiMAX. The IEEE 802.11 WLAN has become a dominating technology due to its low cost and ease of implementation. But, transmitting video over WLANs in real time remains a challenge because it imposes strong demands on video codec, the underlying network, and the Media Access Control (MAC) layer. This paper presents a cross-layer mapping algorithm to improve the quality of transmission of H.264 (a recently-developed video coding standard of the ITU-T Video Coding Experts Group) video stream over IEEE 802.11e-based wireless networks. The major goals of H.264 standard were on improving the rate distortion and the enhanced compression performance. Our proposed cross-layer design involves the mapping of H.264 video slices (packets) to appropriate access categories of IEEE 802.11e according to their information significance. We evaluate the performance of our proposed cross-layer design and the results obtained demonstrate its effectiveness in exploiting characteristics of the MAC and application layers to improve the video transmission quality.     

无线局域网视频流组播优化机制

针对网络电视业务的802.11无线局域网数据传输问题,提出一种视频流组播优化机制,基于视频帧区分的方法,对关键帧I帧采用可靠组播机制传输,对非关键的B帧和P帧采用组播机制传输。仿真结果表明,该机制可以在丢帧率和数据延迟之间取得较好的折中,尤其是在无线网络带宽不足的情况下,能够有效提高数据传输后视频的观看质量。     

远程半自主机器人监控系统的设计及实验

主要介绍了危险环境半自主机器人的远程监视和控制系统,采用无线局域网和CDMA 移动通信网络 相结合的方式实现了视频图像数据的传输和远程控制操作．详细介绍了DM642 如何对视频数据进行采集、格式转 换和压缩等操作,以及机器人运动控制结构、机器人控制协议和无线传输协议的设计．最后,就无线图像传输和机 器人无线控制的实验结果进行了分析和讨论.     

降雨对802.11b WLAN室外传输的影响

在广东省最恶劣的气候是降暴雨,研究降雨对WLAN室外传输的影响很有必要。对于802,11bWLAN的固定无线接入系统,导出在自由空间、晴朗天气和降雨时的接收功率表达式。把晴朗天气的接收功率表达式与降雨时的接收功率表达式进行比较,可以得到降雨衰耗的表达式,进而求得降雨衰减系数。研究得出的降雨衰耗和降雨衰减系数值,不仅对WLAN的固定无线接入,而且对移动通信都具有参考价值。     

Adaptive unequal protection for wireless video transmission over IEEE 802.11e networks

Packet loss of video streams cannot be avoided at wireless links for limited wireless bandwidth and frequently changed environments. To provide differentiated Quality of Service (QoS) guarantees between multimedia and data services, IEEE 802.11e was proposed. However, its performance and flexibility need to be further improved. In this paper, after a survey on various modifications of IEEE 802.11e, we formulate the problem of video transmission over IEEE 802.11e networks to help scheme design and performance analysis. Then accompanied with in-depth analysis, an adaptive unequal protection schema is proposed, which is composed of three mechanisms: (1) Insert each video packet into the access category (AC) with the minimum relative queuing delay; (2) Assign each packet dynamically to a proper AC based on several parameters to guarantee the transmission of high priority frames; (3) Apply fuzzy logic controllers to adjust parameters so as to reply quickly to the variation of video data rate, coding structure and network load. Finally, regarding MPEG-4 codec as the example, we perform extensive evaluations and validate the effectiveness and flexibility of proposed scheme. Simulations are divided into WLAN and multihop parts, involving different video sequences and various traffic modes of data streams. Beside performance comparison between proposed scheme and other ones, influence of parameter setting and combination with routing algorithms are also evaluated.     

Columbia's VoD and Multimedia Research Testbed with Heterogeneous Network Support

This paper reports our progress in developing an advanced video-on-demand (VoD) testbed, which will be used to accommodate various multimedia research and applications such as Electronic News on Demand, Columbia's Video Course Network, and Digital Libraries. The testbed supports delivery of MPEG-2 audio/video stored as transport streams over various types of networks, e.g., ATM, Ethernet, and wireless. Both software and hardware video encoders/decoders are used in the testbed. A real-time video pump and a distributed application control protocol (MPEG-2's DSM-CC) have been incorporated. Hardware decoders and set-tops are being used to test wide-area video interoperability. Our VoD testbed also provides an advanced platform for implementing proof-of-concept prototypes of related research. Our current research focus covers video transmission with heterogeneous quality-of-service (QoS) provision, variable bitrate (VBR) traffic modeling, VBR server scheduling, video over Internet, and video transmission over IP-ATM hybrid networks. An important aim is to enhance interoperability. Accommodation of practical multimedia applications and interoperability testing with external VoD systems has also been undertaken.