RS码在水声数据无线传输中的应用研究

在介绍RS纠错编码原理的基础上,将其应用于水声数据的无线传输中.在仿真环境以及联机实验中,对RS码应用前后的纠错效果进行了分析比较.结果表明,在纠错范围内,水声数据无线传输的可靠性得到了有效提高.     

无线ATM网络上的一种新的适配层协议

提出了一种新ATM适配层的传输协议(AAL_UDP)及它的设计方法，主要的设计思想是在AAL不丢弃包、采用序列号的机制实现头保护功能；使用FEC(前向纠错)的纠错机制。     

宽带VSAT卫星通信平台实现IP组播的应用分析

本文在分析了宽带VSAT卫星通信特点的基础上,在应用层采用前向纠错(FEC)技术实现可靠IP组播。通过仿真实验对FEC的性能进行了研究。结果表明,越是在通信质量差的环境下(雨区),虽不能实现完全意义上的可靠性,FEC对性能的改善越明显。     

OFDM系统中的差错控制技术

基于802．11a的无线局域网将OFDM作为重要技术。为了实现信息的可靠传输，采用前向纠错（FEC）或自动重传请求（ARQ）的差错控制方法以确保一定的服务质量（QoS）。本文分析了OFDM系统中采用的几种FEC和混合ARQ（HARQ）机制的性能，并总结了OFDM系统中的差错控制原则。     

一种面向运营级以太网的自适应前向纠错方法

相对于传统以太网,现有的以太网物理信道已发生巨大变化.运营级以太网则对以太网信道提出了更高的要求,在运营级以太网应用环境下,采用适当机制提高以太网信道可靠性是必要的.在IEEE802.3标准帧结构的基础上,提出了一种包含前向纠错(FEC)机制的帧结构,并阐述了基于该帧结构的FEC方法.该方法除实现纠错功能外,还具有检测信道性能并自适应调节FEC配置的机制,使得可以在保障纠错性能的基础上尽可能减少FEC带来的开销.并且使用该方法的以太网接口能够与普通以太网接口互通互联以实现后向兼容.对该方法的性能进行了透彻的分析,证明该方法可行.设计了网络设备实现该FEC方法,并搭建测试拓扑对该方法进行评测,测试结果表明,该方法可以实现预期功能.     

基于丢包率预测的视频传输纠错算法

为解决视频图像在互联网中进行传输时,其质量易受网络丢包率、时延等因素的影响而显著降低的问题,提出了一种基于丢包率预测的视频传输纠错算法。该算法采用隐马尔可夫模型预测网络丢包率,根据丢包率的大小自适应地选择FEC或ARQ对视频图像进行纠错操作。当预测出的丢包率较高时,为避免FEC算法在丢包率较高时降低带宽利用率,采用选择性ARQ算法恢复丢失的视频数据包,并通过限制其重传次数使视频传输的实时性得到了保证;当预测出的丢包率较低时,则采用优化了RS冗余值的FEC算法进行纠错操作。在OPNET modeler中进行的仿真实验表明,与HARQ算法相比,使用该纠错算法,视频图像的PSNR的平均值提高了1.6 dB,平均时延减少了0.24 s左右。该算法不但降低了视频传输的平均时延和丢包率,而且提高了接收端视频图像的重建质量,具有复杂度低、实现简单的特点。     

ATM中的VLAN

ATM是局域网主干的一种主要选择,它在多媒体业务的传输上具有良好的性能,而VLAN近年来在国内外的局域网中也得到了日益广泛的应用。文章讨论了利用ATM作主干的局域网中的VLAN的设置,然后又提出并分析了几种路由选择方案,并举例加以说明。     

基于前向纠错技术的视频差错恢复方法

目前在IP分组网中进行视频图像的传输正被日益广泛的应用(如:视频电话、视频会议)。但是,由于IP分组网固有的特点,IP分组包丢失的现象不可避免并极大地影响了视频传输的服务质量。该文采用前向纠错技术(FEC,For-wardErrorCorrection),并对视频传输序列的编解码方式进行改进,实现了一种基于前向纠错技术的视频差错控制和恢复方法。使用这种方法,改善了因分组包丢失对视频传输质量带来的影响。     

过采样滤波器组作为纠错码的阈值新算法

考虑量化噪声和信道噪声,搭建基于过采样滤波器组OFBS(Oversampled Filter Banks)的联合信源信道编码系统,研究系统的传输检错纠错性能。提出新的阈值选取方法,该方法是基于贝叶斯假设检验为理论依据的,能根据实际信号和噪声统计特性做实时分析,得出适当的阈值。通过Matlab对系统进行仿真,结果表明信道在不同的转移概率条件,OFBS作为纠错码的阈值新算法的计算复杂度低,并且有很好的检错纠错性能。通过对一维信号的纠错,信号的峰值信噪比平均提高1到2 db。     

基于纠错码和小波变换的彩色图像水印算法

为了提高数字水印的鲁棒性和降低传输过程中的差错,在研究将纠错编码应用于数字水印的基础上, 提出了一种基于BCH 码（或汉明码）和小波变换的彩色图像数字水印算法．该算法利用BCH 码（或汉明码）的纠 错性能,对水印图像进行混沌置乱预处理,实现了彩色图像中数字水印的嵌入和提取．仿真实验结果表明该算法具 有良好的不可见性,而且能抵抗多种攻击,比未采用纠错编码的同一水印算法具有更好的鲁棒性,且基于BCH 码 的算法性能要优于基于汉明码的算法．     

使用简单缓冲管理和选择性丢弃增加ATM／B—ISDN的吞吐量的算法

首先介绍了ＡＲＱ这两种差错控制策略的基本思想,然后从ＡＴＭ网络通信的性质和特点出发,提出ＦＥＣ策略能更好地适应目前日益广泛的多媒体应用,并介绍了一种提高ＦＥＣ性能的守门员加看门人算法。     

An Integrated Framework for Efficient Transport of Real-Time MPEG Video over ATM Best Effort Service

This paper describes a framework for the transport of real-time multimedia traffic generated by MPEG-2 applications over ATM networks using an enhanced UBR best effort service (UBR+). Based on the factors affecting the picture quality during transmission, we propose an efficient and cost-effective ATM best effort delivery service. The proposed framework integrates three major components: 1) a dynamic frame-level priority assignment mechanism based on MPEG data structure and feedback from the network (DexPAS), 2) a novel audio-visual AAL5 SSCS with FEC (AV-SSCS), and 3) an intelligent packet video discard scheme named FEC-PSD, which adaptively and selectively adjusts cell drop levels to switch buffer occupancy, video cell payload type and forward error correction capability of the destination. The overall best-effort video delivery framework is evaluated using ATM network simulation and MPEG2 video traces. The ultimate goal of this framework is twofold: First, minimizing loss of critical video data with bounded end-to-end delay for arriving cells and second, reducing the bad throughput crossing the network during congestion. Compared to previous approaches, performance evaluation shows a good protection of Predictive coded (P-) and Bi-directional Predictive coded (B-) frames at the MPEG video slice layer.     

A robust method for soft IP handover

Multimedia streaming over wireless networks - often called mobile multimedia streaming lets users access music, movie, and news services at any time, regardless of location. Given that multimedia streaming is a key goal of third-generation and future wireless networks, vendors will soon deploy streaming clients in advanced mobile terminals. Current mobile terminals, however, fail to adequately support mobile multimedia communication because wireless networks have high packet-loss rates. To eliminate packet loss during handover, we use a packet path diversity scheme and an end-to-end bicasting mechanism that enables soft IP handover. To offset wireless errors, we use a forward error correction (FEC) scheme and embed it in the bicasting mechanism. Our bicasting method encodes the data stream and then splits it, providing more effective diversity than general bicasting, which sends the same data down both paths.' To support our method, we propose the mobile multimedia streaming protocol (MMSP), a new transport-layer protocol that supports multihoming and bicasting in combination with FEC.     

Scalable Video Multicast Using Expanding Window Fountain Codes

Fountain codes were introduced as an efficient and universal forward error correction (FEC) solution for data multicast over lossy packet networks. They have recently been proposed for large scale multimedia content delivery in practical multimedia distribution systems. However, standard fountain codes, such as LT or Raptor codes, are not designed to meet unequal error protection (UEP) requirements typical in real-time scalable video multicast applications. In this paper, we propose recently introduced UEP expanding window fountain (EWF) codes as a flexible and efficient solution for real-time scalable video multicast. We demonstrate that the design flexibility and UEP performance make EWF codes ideally suited for this scenario, i.e., EWF codes offer a number of design parameters to be ldquotunedrdquo at the server side to meet the different reception criteria of heterogeneous receivers. The performance analysis using both analytical results and simulation experiments of H.264 scalable video coding (SVC) multicast to heterogeneous receiver classes confirms the flexibility and efficiency of the proposed EWF-based FEC solution.     

An adaptive QoS guaranteeing MAC protocol for real-time traffic in TDMA-based wireless ATM networks

This paper presents a new media access control (MAC) protocol based on forward error control (FEC), which is appropriate for supporting real-time traffic with strict QoS requirements in wireless ATM networks. As the channel BER in wireless environments is very high and varying 10⁻⁵–10⁻², previous schemes that use powerful FEC have combated to overcome this noisy channel condition at the cost of valuable bandwidth. As most previous works have been dedicated to maximize the channel efficiency, they were not able to meet QoS requirements of real-time applications in wireless networks. A new MAC protocol proposed in this paper is designed to guarantee the throughput requested by a real-time traffic user while keeping the bandwidth consumption at a minimum. The proposed scheme is for a TDMA system and uses adaptive FEC. We analyze the wireless channel and model it as a two-state error control system to design an efficient MAC protocol. We use simulation experiments to show how the proposed scheme provides QoS guarantees, and compare it with the CDMA system in terms of capacity, i.e. the number of users that can be supported.     

QoS support for per-flow services: POS vs. IP-over-ATM

Packet-over-Sonet and IP-over-ATM are two ways to build high-speed Internet backbones. The work presented maps the parameters for Internet-standard integrated services onto ATM technical parameters and quantifies the performance of each architecture in terms of admissible connections carrying multimedia traffic. Results suggest that ATM networks will not be competitive with pure IP infrastructures over the long term     

The Washington University multimedia system

The Washington University multimedia system (MMS) is a complete multimedia system capable of transmitting and receiving JPEG-compressed video, CD-quality audio, and high-resolution radiological images, in addition to normal network traffic, over the Washington University broadband ATM network. The MMS consists of an ATMizer and three multimedia subsystems. The ATMizer implements the host interface, the interface to the ATM network, and the interface to the three multimedia subsystems. This paper describes the architecture of the MMS, the software used with the system, and the applications which have been developed to demonstrate the capability and applicability of broadband ATM networks for multimedia applications.     

Concurrent multipath transmission combining forward error correction and path interleaving for video streaming

Video streaming is a popular application on next generation networks (NGNs). However, video streaming over NGNs has many challenges due to the high bit error rates of these networks. Forward error correction (FEC) is often applied to improve the quality of video streaming. However, continuous lost packets decrease the recovery performance of FEC protection in NGNs. To disperse continuous lost packets to different FEC blocks, we propose a concurrent multipath transmission that combines FEC with path interleaving. Our proposed control scheme adaptively adjusts the FEC block length and concurrently sends data interleaved over multiple paths. Experimental results with our approach show improved packet loss and signal to noise ratio performance.     

Adaptive hybrid error correction model for video streaming over wireless networks

The Hybrid ARQ (HARQ) mechanism is the well-known error packet recovery solution composed of the Automation Repeat reQuest (ARQ) mechanism and the Forward Error Correction (FEC) mechanism. However, the HARQ mechanism neither retransmits the packet to the receiver in time when the packet cannot be recovered by the FEC scheme nor dynamically adjusts the number of FEC redundant packets according to network conditions. In this paper, the Adaptive Hybrid Error Correction Model (AHECM) is proposed to improve the HARQ mechanism. The AHECM can limit the packet retransmission delay to the most tolerable end-to-end delay. Besides, the AHECM can find the appropriate FEC parameter to avoid network congestion and reduce the number of FEC redundant packets by predicting the effective packet loss rate. Meanwhile, when the end-to-end delay requirement can be met, the AHECM will only retransmit the necessary number of redundant FEC packets to receiver in comparison with legacy HARQ mechanisms. Furthermore, the AHECM can use an Unequal Error Protection to protect important multimedia frames against channel errors of wireless networks. Besides, the AHECM uses the Markov model to estimate the burst bit error condition over wireless networks. The AHECM is evaluated by several metrics such as the effective packet loss rate, the error recovery efficiency, the decodable frame rate, and the peak signal to noise ratio to verify the efficiency in delivering video streaming over wireless networks.