稀疏分光配置OBS网络中的多播机制*

针对在稀疏分光配置的光突发交换（OBS）网络中进行多播的问题,提出了一种基于优先级的共享多播机制。该机制对包含相同分光节点的业务进行汇聚,并且在资源预约过程中引入了优先级来区分主干链路和分支链路,保证多播树的主干链路能优先抢占资源。通过仿真发现,相比传统多播机制,该方式能减少多播业务的丢包率和冗余包的数量,提高资源利用率。     

基于ACL的蓝牙音频应用模型及算法研究

论述了蓝牙协议的体系结构、核心协议、蓝牙传输机制、硬件模块的组成和部分多媒体音频格式。针对基于同步SCO链路的典型蓝牙音频应用模型所存在的一些固有缺陷,提出了一种基于ACL异步链路的新型BRTAAM蓝牙音频应用模型及相应的BRTATP算法,详细地阐述了该算法的同步原理及数据分组格式,最后指出了进一步的研究目标。     

基于ACL的蓝牙音频应用模型及算法研究

论述了蓝牙协议的体系结构、核心协议、蓝牙传输机制、硬件模块的组成和部分多媒体音频格式.针对基于同步SCO链路的典型蓝牙音频应用模型所存在的一些固有缺陷,提出了一种基于ACL异步链路的新型BRTAAM蓝牙音频应用模型及相应的BRTATP算法,详细地阐述了该算法的同步原理及数据分组格式,最后指出了进一步的研究目标.     

蓝牙V2.0+EDR标准的SCO/eSCO语音测试系统开发

现有的蓝牙语音专用测试系统价格昂贵、系统复杂、完全依赖进口.针对研究机构和生产厂商对保证蓝牙语音测试效率和性能基础上最小化测试成本的均衡考虑,本文开发了成本较低的蓝牙V2.0 EDR标准语音测试系统,该系统可以完成必要的蓝牙SCO/eSCO语音链路测试,而不依赖于进口测试设备.     

ATM网多媒体业务传输中的前向纠错研究

与传统的闭环纠错技术相比 ,前向纠错技术 (FEC)更适用于 ATM网多媒体业务传输 .本文对几种主要的FEC机制进行了定性分析 ,得到了评价其性能的参数并进行了比较 ;深入探讨了纠错所在层次的问题 ,对信元级 FEC和包级FEC的性能进行了分析和比较 ,得到了一些重要结论 .本文的研究对 ATM网多媒体业务传输研究具有指导意义     

基于多波动尺度的两层包级自适应抽样

在高速Internet链路的流量测量中,包抽样技术能有效减少被测数据量以节省各种可用资源。文章关注如何提高流量突发和波动周期的抽样精度,提出了一种基于多波动尺度的两层包级自适应抽样方法。该方法能够根据当前流量的突发频度和波动性动态调节每包抽样概率,调节粒度精细。通过在真实流量跟踪下与静态随机抽样方法的对比,两层自适应抽样方法显示了较强的实时捕获流量速率的波动变化和改善抽样精度的能力。     

蓝牙技术中DRR算法的改进方案和应用

DRR算法是为了解决在路由器中多用户情况下的资源合理分配问题而提出的。由于Bluetooth系统帧长可变以及存在SCO链路时特定的收发时序，使得应用于蓝牙系统上的DRR算法需要作出改进。改进后的算法蓝牙主设备可以根据数据流量的变化，进行业务活动规划，文章首先举出蓝牙业务分派中的实际问题，提出了DRR算法的改进方案，然后对方案进行理论分析，最后仿真结果表明了此算法对系统性能的改善。     

蓝牙Scatternet在足球机器人通信中的研究

本文针对机器人足球比赛中无线通信频率的相互干扰和稳定性差等问题,引入蓝牙技术。详细介绍了蓝牙的两种组网方式,提出基于散射网的构造算法;通过蓝牙技术实现机器人与决策数据库服务器的无线通讯,提高了无线通信方式在机器人足球比赛中的实时性、安全性和抗干扰能力。研究表明,这种方法是行之有效的。     

蓝牙无线链路质量的分析、测试与改善

蓝牙协议定义了灵活的编码方案(检纠与纠错机制),可针对不同的链路质量选用不同的编码方案,并可映射到相应的数据分组格式上,这为可靠的通信提供了有力的保证。文章简要地分析了蓝牙协议中的几种编码方案,重点讨论了编码方案对链路质量的影响并提出了两种链路质量测试方法,最后介绍了链路质量的几种改善技术。     

一种路由器队列调度算法LW-WFQ的研究

针对路由器主动队列调度算法WFQ(Weighted Fair Queuing)在链路拥塞时无法保证低速率实时业务的QoS(Quality of Service)要求以及实时性业务突发时会导致延迟抖动加大的问题,提出了一种队长和权值调整的算法LW-WFQ。该算法增加了自适应队列管理器和应对突发机制,减少了分组的排队等待时间。最后以NS2为平台,对WFQ及LW-WFQ算法的性能进行大量的仿真对比分析,调节并确定合适的参数,实验结果证明LW-WFQ算法在延迟、抖动等方面的性能有一定程度的提高。     

实时视频通信中的自适应前向纠错方案设计

本文针对实时视频通信中的网络丢包问题，提出了一种基于Reed Solomon算法的自适应FEC方案。与以往的静态FEC编解码方案不同，该方案引入一种新的基于SIP／RTP的QoS反馈机制，根据丢包率大小在发送端调整FEC冗余度、整体发送速率以及封包大小来保证服务质量；并针对网络突发丢包情况，在对数据包进行FEC编码时采用了交织技术     

An unequal packet loss resilience scheme for video over the Internet

We present an unequal packet loss resilience scheme for robust transmission of video over the Internet. By jointly exploiting the unequal importance existing in different levels of syntax hierarchy in video coding schemes, GOP-level and Resynchronization-packet-level Integrated Protection (GRIP) is designed for joint unequal loss protection (ULP) in these two levels using forward error correction (FEC) across packets. Two algorithms are developed to achieve efficient FEC assignment for the proposed GRIP framework: a model-based FEC assignment algorithm and a heuristic FEC assignment algorithm. The model-based FEC assignment algorithm is to achieve optimal allocation of FEC codes based on a simple but effective performance metric, namely distortion-weighted expected length of error propagation, which is adopted to quantify the temporal propagation effect of packet loss on video quality degradation. The heuristic FEC assignment algorithm aims at providing a much simpler yet effective FEC assignment with little computational complexity. The proposed GRIP together with any of the two developed FEC assignment algorithms demonstrates strong robustness against burst packet losses with adaptation to different channel status.     

A study of adaptive forward error correction for wireless collaborative computing

This paper addresses the problem of reliably multicasting Web resources across wireless local area networks (WLANs) in support of collaborative computing applications. An adaptive forward error correction (FEC) protocol is described, which adjusts the level of redundancy in the data stream in response to packet loss conditions. The proposed protocol is intended for use on a proxy server that supports mobile users on a WLAN. The software architecture of the proxy service and the operation of the adaptive FEC protocol are described. The performance of the protocol is evaluated using both experimentation on a mobile computing testbed as well as simulation. The results of the performance study show that the protocol can quickly accommodate worsening channel characteristics in order to reduce delay and increase throughput for reliable multicast channels.     

基于Kalman滤波的无线流媒体自适应混合FEC/ ARQ控制策略

提出了一种用于无线实时流媒体传输的数据链路层自适应混合FEC/ARQ控制策略,以显著提高接收方的播放质量。该策略采用跨层设计的方法,基于Kalman滤波器预测当前的网络状态,自适应地调整FEC参数N和ARQ参数Nmax;另一方面,在应用层采用自适应FEC策略,在视频源数据和冗余数据之间动态分配网络带宽。数学分析和仿真验证均表明,该策略能使接收方获得最大的可播放帧率,有效地提高了流媒体传输的可靠性和实时性。     

Cross-Layer Error Control for Multimedia Streaming in Wireless/Wireline Packet Networks

In this paper, we propose a cross-layer error control framework for robust and low delay multimedia streaming in tandem-connected IEEE 802.11 wireless LANs and the Internet. For this network configuration, we model the end-to-end delay and packet loss rate as a function of the automatic repeat request (ARQ) and forward error correction (FEC) error control mechanisms that are employed at the application and wireless link layers. The analytical model is used as the basis of a delay-constrained error control algorithm that adapts the protection level at the application and link layers so that the end-to-end packet loss rate is minimized. With extensive simulations, we validate the efficiency of the proposed cross-layer error control methodology for delay-sensitive pre-compressed video streaming.      

一种改进的高速链路前向纠错编码

在高速链路的可靠传输中,物理层前向纠错的研究主要集中在提高编码的纠错性能,且编码冗余位全部用于纠错校验,难以满足用户在传输中加载定制信息的应用需求。针对这一问题,设计了一种编码利用率更高、灵活性更强的前向纠错编码方案,并通过Matlab和综合工具对性能和开销进行了评估,在不损失编码性能的前提下得到了一系列可以无损加载用户定制信息的前向纠错编码。     

Packet loss resilience using unequal forward error correction assignment for video transmission over communication networks

Forward error correction (FEC) methods have been developed for packet loss resilience in application layer for real-time video transmission over communication networks. In this paper, an efficient packet loss resilience method is proposed using closed form solution for unequal FEC assignment based on a new packet distortion model. We first derive the packet distortion model by investigating the error concealment property and error propagation effect in H.264. To select the source and channel rate minimizing the overall distortion, we present a model-based rate allocation algorithm using the packet distortion model and rate-distortion function. Then we propose the closed form solution for unequal FEC assignment, which uses the packet distortion model and considers channel status information. Simulation results show that the proposed method gives substantial improvement for the received video quality in packet-lossy Internet and wireless network environments, while it requires much less computational complexity compared to the previous scheme.     

Combining Media-Specific FEC and Error Concealment for Robust Distributed Speech Recognition Over Loss-Prone Packet Channels

This paper presents a mixed recovery scheme for robust distributed speech recognition (DSR) implemented over a packet channel which suffers packet losses. The scheme combines media-specific forward error correction (FEC) and error concealment (EC). Media-specific FEC is applied at the client side, where FEC bits representing strongly quantized versions of the speech vectors are introduced. At the server side, the information provided by those FEC bits is used by the EC algorithm to improve the recognition performance. We investigate the adaptation of two different EC techniques, namely minimum mean square error (MMSE) estimation, which operates at the decoding stage, and weighted Viterbi recognition (WVR), where EC is applied at the recognition stage, in order to be used along with FEC. The experimental results show that a significant increase in recognition accuracy can be obtained with very little bandwidth increase, which may be null in practice, and a limited increase in latency, which in any case is not so critical for an application such as DSR     

基于集成FEC的可靠多目广播及性能评价

对点对点通信，数据的传输常使用自动重复求技术，而前向纠错多用于半可靠实时传输。然而，ＡＲＱ用于多目广播的性能不佳。