Reducing channel change delay in IPTV by predictive pre-joining of TV channels

One of the major concerns of IPTV network deployment is channel change delay (also known as zapping delay). This delay can add up to 2 s or more, and its main culprits are synchronisation and buffering of the media streams. Proving the importance of the problem is the already significant amount of literature addressing it. We start this paper with a survey of techniques proposed to reduce IPTV channel change delay.Then, by analysing an extensive dataset from an operational IPTV provider - comprising 255 thousand users, 150 TV channels, and covering a 6-month period - we have observed that most channel switching events are relatively predictable: users very frequently switch linearly, up or down to the next TV channel. This fact motivated us to use this dataset to analyse in detail a specific type of solutions to this problem, namely, predictive pre-joining of TV channels. In these schemes each set top box (STB) simultaneously joins additional multicast groups (TV channels) along with the one that is requested by the user. If the user switches to any of these channels the switching latency is virtually eliminated, not affecting therefore user's experience.We start by evaluating a simple scheme, where the neighbouring channels (i.e., channels adjacent to the requested one) are pre-joined by the STB during zapping periods. Notwithstanding the simplicity of this scheme, trace-driven simulations show that the zapping delay can be virtually eliminated for a significant percentage of channel switching requests. For example, when sending the previous and the next channel concurrently with the requested one, for only 1 min after a zapping event, switching delay is eliminated for close to half of all channel switching requests. Importantly, this result is achieved with a negligible increase of bandwidth utilisation in the access link. Other more complex schemes where user behaviour is tracked were also evaluated, but the improvement over the simple scheme was insignificant.     

金属基陶瓷复合材料的激光热冲击破坏效应

 研究了激光热冲击条件下静态受拉Sic颗粒增强6061铝合金材料的热断裂行为。热冲击用的激光束的脉宽分别为1.0ms和250μs, 激光束辐照在缺口的根部附近。对于热冲击下裂纹的产生及扩展进行细致的宏、微观观察,发现裂纹的产生和扩展的机制是不相同的。     

VDL4:一种新型航空VHF数据链

甚高频(VHF)数据链在当今航空通信中具有十分重要的作用。目前航空数据链各异,并各具优势。文中主要论述VDL4,首先介绍了其基本设备结构,说明了协议的层次模型,然后分析了VDL4的时隙选择、网络接入、信道管理等关键技术,最后将它和其余VDL模式数据链进行了比较,从而说明VDL4是一种能满足新航行系统需求、极具竞争力的航空数据链。     

量子通信

介绍了一种最新的通信理念——量子通信。通过对量子通信与常用光波通信的比较，说明了量子通信具有信息容量大，可以进行无破坏检测，及把信息同时传输给多个受信等明显的优势。同时介绍了量子通信国内外最新的研究动态。目前此项通信技术还处在理论完善和试验阶段。     

The modulo-lattice channel: the key feature in precoding schemes

Precoding for transmission over channels with interference known at the transmitter is reviewed. In contrast to what is usually discussed in literature, precoding employing higher-dimensional lattice quantization for generating the transmit signal is assessed. It is shown that thereby the gap between low-complexity schemes using scalar modulo reductions and theoretical asymptotic results assuming hypothetical optimum quantization operations can be bridged. In this paper, capacity curves obtained from numerical calculations, and approximations to the capacity are provided for various lattices. Moreover, the role of appropriate scaling at transmitter and receiver is discussed in detail.     

视频后期制作网中的网络和存储技术

介绍了非线性视频网络在数据传输和存储方面的特殊要求，说明了网络技术和存储技术并做了分析和比较，记述了河南电视台视频后期制作网采用的网络和存储技术及设计和实施。     

Land mobile satellite communication channel model for simultaneous transmission from A land mobile terminal via two separate satellites

There are certain data services that could use transmit-only land-mobile satellite communication terminals. Such terminals would not be able to receive acknowledged messages and transmit them onward. Thus it is of interest to study alternative means of improving the system reliability. In this paper we propose the use of transmission to two satellites separated in azimuth and elevation in order to improve the reliability of throughput. We have investigated the improvements by building upon the model proposed by Lutz for land mobile satellite communications via one satellite, and extended this using measurements of the shadowing coefficient in different areas (suburban, countryside and city) to two separated satellites. The measured data is used to produce an empirical model of the equivalent shadowing coefficient variations with the separation angle variation between two satellites. The results show good agreement with the shadowing coefficients produced by the Lutz model for a single satellite. The degree of improvement produced by using two separated satellites in the different environments, in terms of bit rate and probability of the received power is given.     

一种基于神经网络的矢量量化零冗余度信道编码方法

本文提出一种新的基于神经网络的矢量量化零冗余度信道编码方法,该方法能有效地降低矢量量化编码系统在有噪信道下的平均失真。     

Résolution des équations de dispersion–diffusion en présence de forts gradientsResolution of advection–diffusion equation in presence of sharp gradient

In order to resolve the convection terms in the simulation of coastal flows, we propose a numerical method based on the Total Variation Diminishing scheme completed with the Artificial Compression Method to reduce the artificial diffusion and to sharpen the tracer profile in strong gradient regions. This method was applied successfully at discontinuous regions, but out of these regions a limitation of its application is necessary. An application is made to estimate the width of the fresh water band in the Eastern English Channel. To cite this article: C. Sart et al., C. R. Mecanique 330 (2002) 159–165.     

离子注入中的沟道效应控制

离子注入中的沟道效应使注入离子在深度上的控制变得很困难，并使SHEET值的均一性恶化，本文借助计算机模型。对注入剂量，注入能量，硅片基板方位，硅片表面薄膜氧化层厚度变化时，研究分析了注入沟道效应的相应变化。