A network condition classification scheme for supporting video delivery over wireless Internet*

INTRODUCTION Real-time video transport over wireless Internet faces many challenges due to the heterogeneous en- vironment including wireline and wireless networks. Fig.1 shows a typical end-to-end video transport in- volving wireline and wireless networks. The video transport may suffer from many problems such as wireline network congestion and wireless multi-path fading, resulting in high packet loss-rate, and causing severe video quality degradation. To maintain the optimal video quali…     

Video quality based link adaptation for low latency video transmission over WLANs

INTRODUCTION Low latency video transmission is very de manding in terms of the performance of all layers i the protocol stack. Over the last decade, research ha focused on enhancements of each individual laye without considering cross-layer interactions. Adapt ing video coding to the channel/network condition and technologies (and vice versa) (Girod et al., 2002 via the cross-layer exchange of information has onl recently been investigated. van der Schaar et al.(200 developed a cross-laye…     

Enhanced cooperative packet retransmission employing joint cooperative diversity and symbol mapping diversity

A joint cooperation diversity and symbol mapping diversity （SMD） strategy is proposed for cooperative packet retransmission system with high-order modulation such as 16QAM. Substantial SER/BER （symbol error rate/bit error rate） gains result from multiple packet transmissions over independent paths and distinct bit-to-symbol mappings for each packet transmission. The SER/BER performance of relay assisted retransmission system is analyzed. Simulation results show that the joint-diversity strategy can provide more BER gains than other relaying strategies （i.e., decode-and-forward and constellation rearrangement relaying strategies） when no relay makes a decision error; but if some relays make decision errors, the joint-diversity strategy outperforms other relaying strategies only when the relays are closer to the source than to the destination.     

An embedded packet train and adaptive FEC scheme for effective video adaptation over wireless broadband networks

INTRODUCTION With the emergence of wireless technology, various multimedia services, e.g., audio and/or video, are reaching us today through portable devices any- time, anywhere and even more increasingly accessi- ble in the near future. High quality video streaming over wireless IP is one of the most attractive applica- tions by ongoing deployment of wireless local area network (WLAN) hotspots and even powerful Wi- MAX mobile coverage. However, the present Internet is not providing a…     

避免分组丢失切换方法

针对基本移动IP协议虽然简单但只适用于大范围、低速的情况，提出了一种新的微观移动IP切换方法——避免分组丢失切换方法．该切换方法通过在基站处增加缓存以及利用IP分组的标识，将切换过程中分组丢失减少至最小．并给出了该切换方法所适用的分层全IP网络结构及其切换过程，对基站缓存的大小、切换带来的网络负荷、切换延时等也进行了分析．仿真和分析结果表明最小分组丢失切换方法适用于快速移动、频繁切换的环境．     

Ad hoc网络中一种自适应的负载均衡机制

An adaptive load balancing scheme is proposed to balance the load in ad hoc networks. The new scheme can be applied in most on-demand routing protocols resulting in significant performance improvement. The proposed scheme is applied to the ad hoc on-demand distance vector (AODV) routing protocol. Simulation results show that the network load is balanced on the whole, and performance in packet loss rate, routing overhead and average end-to-end delay is also improved.     

Modeling TCP performance with proxy and ARQ

INTRODUCTION The convenience of wireless communications has led to increasing use of wireless networks for civilian and critical applications. With the advent of Internet technology and the increasing popularity of wireless data devices, the wireless industry is evolv- ing its core networks toward IP-based networks. It will be necessary to integrate the wireless networks and the existing wired networks into the Internet. TCP has been the predominant transport protocol used in the wired …     

A novel OFDM transmission scheme with length-adaptive Cyclic Prefix

INTRODUCTION In broadband wireless communication, thdelay spread caused by channel multi-path fadinwill usually introduce serious Inter-Symbol Interference (ISI) to the receiver. To counteract the ISIthe high-efficiency Orthogonal Frequency DivisioMultiplexing (OFDM) modulation first splits thhigh-rate data stream into a number of parallesub-streams and modulates them onto differenorthogonal sub-carriers and thus lower the symborate, and then add a Cyclic Prefix (CP) to the h…     

A novel OFDM transmission scheme with length-adaptive Cyclic Prefix

Conventional OFDM transmission system uses a fixed-length Cyclic Prefix to counteract Inter-Symbol Interferences(ISI)caused by channel delay spreading under wireless mobile environment. This may cause considerable performance deterioration when the CP length is less than the channel RMS delay spread,or may decrease the system power and spectrum efficiency when it is much larger. A novel Orthogonal Frequency Division Multiplexing(OFDM)transmission scheme is proposed in this paper to adapt the CP length to the variation of channel delay spread. AOFDM-VCPL utilizes the preamble or pilot sub-carriers of each OFDM packet to estimate the channel RMS delay spread; and then uses a criterion to calculate the CP length,which finally affects the OFDM transmitter. As illustrated in the simulation section,by deploying this scheme in a typical wireless environment,the system can transmit at data rate 11.5 Mb/s higher than conventional non-adaptive system while gaining a 0.65 dB power saving at the same BER performance.     

Video over IP using standard-compatible multiple description coding: an IETF proposal

INTRODUCTION Communication networks are growing quickly. Throughput, delays and losses become unpredictable because of heterogeneity and congestion. This results in lack of quality of service. Today’s solution is based on standard video codecs (as MPEG-2) that do not allow scalability and yield low quality at low bit-rates, complex forward error correction (FEC) codes that are not easily used with time-varying channels and must be set to face the worst case, and automatic repeat re- q…     

A novel MAC mechanism to resolve 802.11 performance anomaly

In the 802.11b networks, the guarantee of an equal long-run channel access probability causes performance anomaly in a multi-rate wireless cell. Much interest has been involved in this issue and many effective mechanisms have been proposed. The usual MAC layer solutions include the initial contention window adaptation, the maximum transfer unit size adaptation and the packet bursting. In this paper, we propose a novel approach which introduces a new parameter called the transmission prob- ability pt to the legacy protocol. By adjusting pt according to the transmission rate, the proposed scheme can solve the performance anomaly problem cleanly. Throughput analysis and performance evaluation show that our scheme achieves significant im- provement in the aggregate throughput and the fairness.     

P2P应用层多播协议模型RLP2P的仿真与分析

数据通道质量、鲁棒性和控制开销是表征应用层多播性能质量的三个重要指标.对可扩展基于域的多层结构P2P应用层多播协议模型RLP2P的综合性能进行了仿真分析,通过与Narada应用层多播协议模拟对比分析表明,数据通道的伸展率优于Narada协议,增加5%;在链路和节点上产生的压力比Narada协议减少25%以上,且分布均匀,特别是多播组成员增加时尤其显著;控制开销比Narada协议减少60%以上,在域内节点数为100,其控制开销小于等于1Kbps,且维持在一个很低的水平;节点加入和非正常离开时的最大丢包率小于1%;Query消息平均延迟为8.5×10-2s,减少延迟达30%.     

Rate-distortion optimized frame dropping and scheduling for multi-user conversational and streaming video

INTRODUCTION Video packets are transmitted over the Internet using a best-effort service. Therefore, a large number of simultaneous video streams or cross traffic arriving at a network node (e.g. a multimedia gateway) may sometimes exceed the node’s forwarding capacity, i.e., the incoming data rate may exceed the outgoing data rate at the node. In this paper, we consider a scenario where M streaming videos and N conversa- tional videos pass through a network node with lim- ited forwardi…     

一种新颖的基于FGS的发射能量最小化算法

1Introduction Inamobilecommunicationsystem,themobile phoneusesabatterytosupplyenergy.Sincethebat teryenergyislimited,minimizationofenergycon sumedinprocessingandtransmission[1]inmultimedia communicationbecomesanimportantconsideration.Hereweconsidertransmissionenergy.Twofactors areconcernedwithtransmissionenergy,i.e.,trans missionpowerandtransmissiontime,theformeris basedonchannelcharacteristicandconsumerrequire ments,whilethelatterisdecidedbythenumberof bits.Researchonthesetwotopicshasreceive…     

卫星IP网技术

进一步发展Internet业务需要增大带宽并且要有移动性,因而卫星网与IP网结合成了热门话题.针对卫星网的信道差错率高、传播延迟长和信道不对称性对TCP传播性能有不良影响,介绍了前向纠错和自动重传两种链路差错控制方案和对TCP的改进.     

模糊变结构时延控制算法及在AQM中的应用

研究了带有延迟时间补偿的模糊变结构控制算法，分析了模糊变结构控制中积分因子对于时延因子的补偿机理，并基于网络拥塞路由器中TCP连接的线性化模型设计了适用于主动队列管理的时延控制算法．最后讨论了该控制算法的实现问题和参数整定，进行了仿真实验．对于TCP主动队列管理的性能分析和比较试验表明，本算法在RTT和TCP会话数量变动时保持了良好性能和鲁棒性，在丢包率、吞吐量和缓冲波动方面相比其他类似方案有明显的性能优势．     

一种用于无线ATM网络多媒体业务的CAC方案

本文提出一种用于无线ATM网络多媒体业务的CAC方案。在该方案中，延迟约束用于可变比特速率，抖动约束服务质量(QoS)用于不变比特速率，从而保证了所有通信预定义的服务质量要求。为了减少切换掉话率，CAC方案赋予切换呼叫的优先权比新呼叫的高，并预约适当资源用于潜在的切换呼叫。CAC方案中的资源预留是通过用户移动信息来确保资源有效利用。分析结果表明，所提出的CAC方案能取得较低的切换掉话率和较高的系统资源利用率。     

An adaptive joint source and channel coding scheme for H.264 video multicasting over wireless LAN

INTRODUCTION Video multicasting over wireless local area net- work (WLAN) (IEEE Standard 802.11, 1997) enables the distribution of live or pre-recorded programs to many receivers efficiently. An example application is to redistribute TV programs or location-specific in- formation in hot spots such as airport. Users can watch their favorite TV programs on mobile devices while browsing the Internet. For enterprise applica- tions, an example is multicasting video of a lecture or trainin…     

An adaptive FEC to protect RoHC and UDP-Lite H.264 video critical data

INTRODUCTION Recommendation H.264 was approved by ITU-T in May 2003 and the approved draft specifi cation is available for public review (Wiegand, 2003) The H.264 video codec has a very broad application range that covers all forms of digital compressed video from low bit rate Internet streaming applica tions to HDTV broadcast and digital cinema applica tions with near lossless coding. About 50% band width would be saved by using H.264 when compared to the existing most efficient com…     

基于链路层切换技术的网络层快速切换方法

提出了一种新的网络层快速切换方法,该方法在链路层同步转发切换方法的基础上通过增加两个网络层切换实体来实现网络层快速切换,实现了IP移动检测的零时延。仿真结果表明,该基于链路层切换技术的网络层快速切换能够减少结点在子网间切换带来的时延,从而满足了实时应用的要求。