Raptor码译码算法的改进方案

喷泉码是一类重要的纠删码,特别是Raptor码,由于其非固定码率、逼近信道容量、可以有效纠删等方面的内在特点,非常适合作为应用层FEC而使用到各类系统中。主要就Raptor码的译码算法展开深入的讨论,在介绍现有译码算法的基础上,提出了Raptor码译码算法的优化思路,它能更好的平衡译码失败率和译码计算复杂度两个指标之间的关系,以更好的适用于某些特定应用场景的需要。     

无线传感器网络差错控制技术的能效分析

对自动请求重传(ARQ)技术和前向纠错(FEC)技术的能效进行了分析,提出在无线传感器网络中使用Chase合并混合自动请求重传(HARQ)方案实现自适应差错控制,以满足无线传感器网络的不同链路对差错控制方案的差异性要求.仿真结果表明,Chase合并HARQ为整体最优的差错控制方案.     

SIP协议在NGN中的应用

结合用于信息传输、战地指挥的跳频军用无线分组通信网络的研究课题,首先分析了有线领域传输的HDLC链路协议技术在传输中差错控制方面存在的问题;然后在此基础上提出了基于无线传输业务类型的改进HDLC链路差错控制方案,针对不同类型的业务采用前向纠错FEC或FEC与自动反馈重传ARQ相结合的技术。在该差错控制方案中,设计了信道级FEC和信息级FEC来保证实时型业务所需。     

前向纠错在高速光网络系统中应用分析研究

前向纠错（FEC）能够较好地提高光网络性能,如增加光通信系统的传输距离,减少光端机发射功率,降低接收机灵敏度等。文中理论分析并比较了FEC在WDM光网络中两种应用形式（带内FEC和带外FEC）的纠错性能特性,满足不同速率高速光网络系统的应用需要,可以采用相应的FEC应用形式。     

FEC在高波动性网络中的应用研究

前向纠错(FEC)方式可以有效提高网络数据传输的可靠性。喷泉码(Digital Fountain)作为其中较先进的一种,在数字视频广播(DVB)和网络通信等领域有着广泛的应用。设计了RS码和Raptor码的性能实验,验证在较高丢包率下的解码性能。提出了结合重传机制的Raptor码多路传输方案。实验证明,对于高波动性网络中的UDP传输,使用Raptor码能以较低的解码开销获得稳定的解码成功率,而ARQ-Raptor多路传输方案能有效地利用多路带宽进行可靠的数据传输。     

FEC在高波动性网络中的应用研究北大核心

前向纠错(FEC)方式可以有效提高网络数据传输的可靠性。喷泉码(Digital Fountain)作为其中较先进的一种,在数字视频广播(DVB)和网络通信等领域有着广泛的应用。设计了RS码和Raptor码的性能实验,验证在较高丢包率下的解码性能。提出了结合重传机制的Raptor码多路传输方案。实验证明,对于高波动性网络中的UDP传输,使用Raptor码能以较低的解码开销获得稳定的解码成功率,而ARQ-Raptor多路传输方案能有效地利用多路带宽进行可靠的数据传输。     

基于无线传输业务类型的HDLC差错控制技术研究

结合用于信息传输、战地指挥的跳频军用无线分组通信网络的研究课题．首先分析了有线领域传输的HDLC链路协议技术在传输中差错控制方面存在的问题;然后在此基础上提出了基于无线传输业务类型的改进HDLC链路差错控制方案,针对不同类型的业务采用前向纠错FEC或FEC与自动反馈重传ARQ相结合的技术。在该差错控制方案中,设计了信道级FEC和信息级FEC来保证实时型业务所需的误比特率,同时采用信道级FEC和信息级ARQ相结合的方式来保证非实时型数据业务所需的服务质量。最后通过分析和计算机仿真,验证该差错控制方案的有效性和可行性。     

RFID定位系统中电子标签发射功率估算

针对一些坑道式地下工程需要实现对工作人员实时管控的需求,构建了基于智蜂(ZigBee)无线传感器网络和射频识别(Radio Frequency Identification,FRID)技术的人员管控系统.电子标签的发射功率估算是人员管控系统设计的重要方面,在分析几种典型无线传播模型的基础上,得出了各模型的优缺点和适用范围.就适于地下工程的分隔损耗模型,分析了电子标签发射功率与无线传播距离和传感器节点接收灵敏度之间的关系,并对有源电子标签所需的最小发射功率进行了估算,结果表明,选用最大发射功率为0 dBm,接收灵敏度为-92 dBm的无线芯片便可以满足有源电子标签的设计需求.     

基于功率分配能量采集的全双工放大转发中继系统

针对三节点放大转发中继系统,研究了基于功率分配能量采集的全双工中继传输方案。在中继配置大规模天线的情况下,提出了三种天线选择方法,并通过合理的假设分别推导了三种天线选择方法的速率的近似闭合表达式,并设计了天线选择模式切换方案。基于三种不同的天线选择方法,该文分析了基于功率分配采集协议中的最优功率分配因子以及不同方案的算法复杂度。最后,通过蒙特卡洛仿真证明了闭合表达式的准确性,并基于发射功率和信道增益分析了三种方案的优缺点。其中在大发射功率的情况下,方案一的性能最优;在小发射功率的情况下,方案二的性能最优;在中等发射功率的情况下,折中的方案三的性能最优。      

无线视频传输中FEC与WZ联合抗误码算法研究

无线视频编码的低抗误性、无线信道带宽的有限性、无线视频业务的高需求决定了高鲁棒性的抗误算法必将成为无线视频通信的核心问题之一.基于FEC与WZ (Wyner-Ziv)两抗误工具的在不同误码率下抗误互补特性,提出了FEC与WZ联合抗误码方案.实验表明:该方案有效地综合了两者优点,提升了平均PSNR.     

Adaptive two-stage FEC scheme for scalable video transmission over wireless networks

In this paper, we present a two-stage forward error correction (FEC) scheme with an enhanced link-layer protocol especially for multimedia data transmission over wireless LANs. At the application layer, packet-level FEC (stage-one) is added across packets to correct packet losses due to congestion and route disruption. Bit-level FEC (stage-two) is then added to both application packets and stage-one FEC packets to recover bit errors from the link layer. Then at the link layer, header-CRC/FEC is used to enhance protection and to cooperate with the two-stage FEC scheme. The proposed scheme thus provides joint protection across the protocol stack. We explore both its bandwidth efficiency and video performance for the highly efficient and scalable MC-EZBC video codec using the network simulator ns-2. Our results show that the proposed scheme can effectively increase application-layer throughput, reduce both end-to-end transmission delay and application bandwidth fluctuation, and significantly improve video performance.     

FEC/FCC技术在运营商网络中的应用研究

通过对视频业务现状和业务质量的分析,结合FEC和FCC技术的特点,以IPTV业务为例,阐述了FEC和FCC技术在江苏电信业务网络中的应用。通过开展实验室测试和现网试点,证明FEC和FCC技术可显著提升IPTV业务使用感知。     

Reliable transmission of high-quality video over ATM networks

The development of broadband networks has led to the possibility of a wide variety of new and improved service offerings. Packetized video is likely to be one of the most significant high-bandwidth users of such networks. The transmission of variable bit-rate (VBR) video offers the potential promise of constant video quality but is generally accompanied by packet loss which significantly diminishes this potential. We study a class of error recovery schemes employing forward error-control (FEC) coding to recover from such losses. In particular, we show that a hybrid error recovery strategy involving the use of active FEC in tandem with simple passive error concealment schemes offers very robust performance even under high packet losses. We discuss two different methods of applying FEC to alleviate the problem of packet loss. The conventional method of applying FEC generally allocates additional bandwidth for channel coding while maintaining a specified average video coding rate. Such an approach suffers performance degradations at high loads since the bandwidth expansion associated with the use of FEC creates additional congestion that negates the potential benefit in using FEC. In contrast, we study a more efficient FEC application technique in our hybrid approach, which allocates bandwidth for channel coding by throttling the source coder rate (i.e., performing higher compression) while maintaining a fixed overall transmission rate. More specifically, we consider the performance of the hybrid approach where the bandwidth to accommodate the FEC overhead is made available by throttling the source coder rate sufficiently so that the overall rate after application of FEC is identical to that of the original unprotected system. We obtain the operational rate-distortion characteristics of such a scheme employing selected FEC codes. In doing so, we demonstrate the robust performance achieved by appropriate use of FEC under moderate-to-high packet losses in comparison to the unprotected system.     

Rate-distortion optimized hybrid error control for real-time packetized video transmission.

The problem of application-layer error control for real-time video transmission over packet lossy networks is commonly addressed via joint source-channel coding (JSCC), where source coding and forward error correction (FEC) are jointly designed to compensate for packet losses. In this paper, we consider hybrid application-layer error correction consisting of FEC and retransmissions. The study is carried out in an integrated joint source-channel coding (IJSCC) framework, where error resilient source coding, channel coding, and error concealment are jointly considered in order to achieve the best video delivery quality. We first show the advantage of the proposed IJSCC framework as compared to a sequential JSCC approach, where error resilient source coding and channel coding are not fully integrated. In the USCC framework, we also study the performance of different error control scenarios, such as pure FEC, pure retransmission, and their combination. Pure FEC and application layer retransmissions are shown to each achieve optimal results depending on the packet loss rates and the round-trip time. A hybrid of FEC and retransmissions is shown to outperform each component individually due to its greater flexibility.     

Joint QoS control for video streaming over wireless multihop networks: A cross-layer approach

In this paper, we propose a novel cross-layer framework for jointly controlling and coding for multiple video streams in wireless multihop networks. At first, we develop a cross-layer flow control algorithm that works at the medium access control (MAC) layer to adjust each link's persistence probability and at the transport layer to adjust flow rates. This proposal is designed in a distributed manner that is amenable to online implementation for wireless networks, and then, a rate-distortion optimized joint source-channel coding (JSCC) approach for error-resilient scalable encoded video is presented, in which the video is encoded into multiple independent streams and each stream is assigned forward error correction (FEC) codes to avoid error propagation. Furthermore, we integrate the JSCC with the specific flow control algorithm, which optimally applies the appropriate channel coding rate given the constraints imposed by the transmission rate obtained from the proposed flow control algorithm and the prevailing channel condition. Simulation results demonstrate the merits and the need for joint quality of service (QoS) control in order to provide an efficient solution for video streaming over wireless multihop networks.     

Rate-distortion based real-time wireless video streaming

This paper presents wireless video streaming techniques that exploit the characteristics of video content, transmission history, and physical layer channels to enable real-time efficient video streaming over wireless networks to a wireless client. The key contribution of the proposed video streaming techniques is the use of rate-distortion based, but simplified, low complexity packet scheduling as well as forward error correction (FEC) rate selection. To this end, we develop an optimization framework that jointly schedules the packets and selects the FEC rates. The rate-distortion optimized packet scheduling and FEC rate selection provides the optimum quality video on the receiver side albeit at a high computational cost. By some intelligent approximations, rate distortion optimized packet scheduling and FEC rate selection technique is transformed into two sub-optimal but low complexity video streaming techniques that can provide high video quality. We perform extensive simulations to understand the performance of our proposed techniques under different scenarios. Results show that, the proposed techniques improve video quality on the average by 4 dB. We conclude that significant benefits to end-user experience can be obtained by using such video streaming methods.     

3D visual experience oriented cross-layer optimized scalable texture plus depth based 3D video streaming over wireless networks

3D video streaming over the mobile Internet generally incurs the inferior 3D visual experience due to the time-varying characteristics of wireless channel. The conventional video streaming optimization methods generally neglect the harmony among different networking protocol layers. This paper proposes a cross-layer optimized texture plus depth based scalable 3D video streaming method to improve the expected 3D visual experience of the user by systematically considering the application layer texture-video/depth/FEC bit-rate allocation, MAC layer multi-channel allocation, and physical layer modulation and channel coding scheme (MCS) selection. In the cross-layer optimization, a networking-related 3D visual experience model which fuses the overlapped retinal view visual quality and depth sensation with mimicking human vision system is established to predict the 3D visual experience under the specific parameter configurations of different protocol layers. The efficiency and effectiveness of the proposed cross-layer optimized 3D video streaming method has been validated by subjective and objective experimental results.     

Graceful Degradation FEC Layer for Multimedia Broadcast/Multicast Service in LTE Mobile Systems

This paper proposes an additional forward error correction (FEC) layer to compensate for the defectiveness inherent in the conventional FEC layer in the Long Term Evolution specifications. The proposed additional layer is called a graceful degradation (GD)‐FEC layer and maintains desirable service quality even under burst data loss conditions of a few seconds. This paper also proposes a non‐delayed decoding (NDD)‐GD‐FEC layer that is inherent in the decoding process. Computer simulations and device‐based tests show a better loss recovery performance with a negligible increase in CPU utilization and occupied memory size.     

A recommended error control architecture for ATM networks withwireless links

This paper provides performance results through analysis and simulation for key error control problems encountered in using wireless links to transport asynchronous transfer mode (ATM) cells. Problems considered include the forward-error correction (FEC) and interleaving at the physical layer, the impact of wireless links on the ATM cell header-error control (HEC) sand cell delineation (CD) functions, the application of data link automatic repeat-request (ARQ) for traffic requiring reliable transport, and the impact of the choice of end-to-end ARQ protocol for reliable service. We conclude that it is very important to make the physical layer as SONET-like as possible through the use of powerful FEC, interleaving, and ARQ. These additional error control measures are especially necessary for disturbed channels because of the degrading effects of the channel on higher-layer functions. A recommended error control architecture is given with tradeoffs