A segment version transcoding for client-centric wireless mobile media streaming

An object segment similarity function is taken into account from the continuous media frames to measure the individual streaming profit of certain segment versions of a media object.Therefore,a new segment version-based transcoding （SVT） mechanism is derived for a quality of service （QoS） of client-centric media streaming in wireless mobile networks.The derived function utilizes the fuzzy similarity of certain segment versions of an object.This mechanism provides the effectiveness of reduction of the stream startup latency among segment versions,and the average access of each version.Thus,the proposed segment version transcoding mechanism reduces packet loss which in turn increases streaming performance and throughput.The performance of the partitioned segment versions is simulated and some segment versions are completed.The simulation results show that the proposed mechanism outperforms the other mechanisms in average cache hit ratio and in average startup latency ratio.     

Chloride ion transmission model under the drying-wetting cycles and its solution

The chloride ion transmission model considering diffusion and convection was established respectively for different zones in concrete by analyzing chloride ion transmission mechanism under the dryingwetting cycles. The finite difference method was adopted to solve the model. The equation of chloride ion transmission model in the convection and diffusion zone of concrete was discreted by the group explicit scheme with right single point （GER method） and the equation in diffusion zone was discreted by FTCS difference scheme. According to relative humidity characteristics in concrete under drying-wetting cycles, the seepage velocity equation was formulated based on Kelvin Equation and Darcy＇s Law. The time-variant equations of chloride ion concentration of concrete surface and the boundary surface of the convection and diffusion zone were established. Based on the software MATLAB the numerical calculation was carried out by using the model and basic material parameters from the experiments. The calculation of chloride ion concentration distribution in concrete is in good agreement with the drying-wetting cycles experiments. It can be shown that the chloride ion transmission model and the seepage velocity equation are reasonable and practical. Studies have shown that the chloride ion transmission in concrete considering convection and diffusion under the drying-wetting cycles is the better correlation with the actual situation than that only considering the diffusion.     

An optimized transmission line model of grounding electrodes under lightning currents

In this paper,an optimized transmission line model(OTL) for modeling transient behavior of grounding electrodes under lightning currents is presented.The soil ionization effect is considered in OTL,and all electromagnetic couplings between different parts of grounding electrode are also considered by selecting the size of segment conductor properly and calculating the mutual coupling parameters between segment conductors accurately.Comparing with the traditional transmission line model,the optimized model can be used to accurately predict the effective length and transient potential rise(TPR) of grounding electrodes.Transient behaviors of grounding electrodes are simulated by OTL and the results are in good agreement with those of the electromagnetic model proposed by Grcev,and experiment results performed by Electricité de France and Geri.Furthermore,non-uniform discharging phenomenon of grounding electrode under lightning current is discussed,and the effective lengths of horizontal grounding electrode under lightning currents are presented.     

Dynamic experiment and numerical simulation of solute transmission in heap leaching processing

Solute transmission in saturated ore heap was studied numerically and experimentally. The convection-diffusion equation (CDE) used to describe the mass transportation in porous media was solved by characteristic difference method to give the distribution of the concentration of ferrous ion in the ore column. To calibrate the computational model, a column test was performed using infiltration of sulfide ferrous solution (the initial concentration is c0=0.04 mol/L) on a 100 cm high column composed of ore particles smaller than 10 mm for 2.5 h. The numerical analysis shows that the results obtained from numerical modeling under the same operating conditions as used for column test are in good agreement with those from experimental procedure on the whole trend, which indicates that the model, the numerical method, and the parameters chosen can reflect the rule of ferrous ion transmission in ore heap.     

PRMA： A new MAC protocol for WLAN

In this paper, a new MAC protocol for WLAN is proposed. The new protocol, which is called PRMA （Priority Rotation Multiple Access） , is based on priority rotation theory. In PRMA, each access cycle consists of a contention period and a data transmission period. During contention period, a node competes for the right to control the channel according to its priority. The winner of contention can control the channel and can send data without collision in data transmission period. Analysis and simulation results show that PRMA is a stable protocol, which means that it can achieve high throughput both under high-load and under low-load conditions.     

Analysis of vehicle powertrain dynamic performance

To study the vehicle dynamic characteristics under typical cycle conditions, a steadystate simulation model of the engine in GTPower is established and verified with engine bench test data. A dynamic model of the engine is then established. A cosimulation with the engine dynamic model in GT-Power and the vehicle transmission model in AMESim is conducted based on the technology of HLA/RTI. The parameter changes of vehicle powertrain in the accelerating process of 0-32km/h, and vehicle typical cycle conditions are studied. The influence laws of the typical parameters influencing vehicle dynamic characteristics are obtained, and a new approach of improving vehicle dynamic characteristics is proposed. The results show that the vehicle powertrain dynamic model can simulate, analyze and predict dynamic changes of vehicle in actual operating conditions and guide powertrain matching and optimization.     

A new constrained-send mechanism to enhance the performance of IEEE 802.11 DCF

In this paper, a modified access mechanism named Constrained-send DCF (CDCF) is proposed to improve the performance of IEEE 802.11 DCF protocol. It is found that, in DCF, the transmission probability is higher than the reasonable value when the node number is greater than 4 under basic access scheme or than 17 under RTS/CTS scheme, and it results in serious collision. To avoid collision of high access loading, a constrained-send probability is introduced at the end of each back off procedure for the station transmitting. The performance of this mechanism is analyzed based on a 2-Dimension Markov analytical model, after that the optimum constrained-send probability is derived. Numerical results show that the CDCF mechanism has much better performance than DCF with respect to both system throughput and average packet delay. And under RTS/CTS scheme, although CDCF slightly improve the throughput performance (due to the natural good throughput performance of RTS/CTS-scheme DCF), it leads to a much better average packet delay performance compared to DCF. The CDCF keeps all the features of the IEEE 802.11 DCF protocol and is quite easy to implement.     

Energy efficiency enhancement of two-way amplifier forward relaying with channel estimation error简

In order to save energy consumption of two-way amplifier forward （AF） relaying with channel estimation error, an energy efficiency enhancement scheme is proposed in this work. Firstly, through the analysis of two-way AF relaying mode with channel estimation error, the resultant instantaneous SNRs at end nodes is obtained. Then, by using a high SNR approximation, outage possibility is acquired and its simple closed-form expression is represented. Specially, for using the energy resource more efficiently, a low-complexity power allocation and transmission mode selection policy is proposed to enhance the energy efficiency of two-way AF relay system. Finally, relay priority region is identified in which cooperative diversity energy gain can be achieved. The computer simulations are presented to verify our analytical results, indicating that the proposed policy outperforms direct transmission by an energy gain of 3 dB at the relative channel estimation error less than 0.001. The results also show that the two-way AF relaying transmission loses the two-way AF relaying transmission loses its superiority to direct transmission in terms of energy efficiency when channel estimation error reaches 0.03.     

Architecture of Multimedia Proxy Caching over the Internet

Streaming media data have strict delay and loss requirements, which cannot be adequately supported by the current Internet. Proxy caching technology is introduced to alleviate the effect of the bottleneck bandwidth on the transporting quality. A new architecture of multimedia proxy caching is given to solve the problem of the traditional Web caching technology for the multimedia streaming. The mixed media management module and the resource management module are added to this architecture, the prefetching and replacement method is studied considering the characteristics of streaming media data, the concept of weighed popularity is given to enhance the exactness of the replacement algorithm.     

Performance analysis of CDMA power control system based on fuzzy prediction

Power control is of paramount importance in combating the near-far problem and co-channel interference in a CDMA cellular system. Due to fast fading and ambient interference in a wireless channel, conventional fixed-step power control schemes have difficulty in compensating for the fast fading channel dynamically and in a timely manner. To acquire flexible power regulation in order to maintain required transmission capacity under the given transmission quality requirement, we propose a hybrid power control scheme which makes full use of the simple fuzzy inference rule refined by an operator in the fuzzy control and prediction property from related previous results in Generalized Prediction Control (GPC). In implementation of this strategy, we classify the fading zone into three levels according to the signal-to-noise-rate (SNR) requirement. In each level the power compensation amount varies with fading gradient and the compensation scheme varies as well. The digital results show that adoption of the fuzzy-GPC power regulation scheme has acquired a reasonable performance improvement when compared with fixed-step and fuzzy schemes. According to theoretic analysis and simulation results,we can conclude that under a variational transmission environment, a flexible power regulation scheme such as fuzzy-GPC is easy to adapt to the environment and thus overcomes the near-far effect and multi-access interference effectively.     

基于等待时间和信道状态的轮询多址协议

提出了基于分组等待时间和信道状态的动态限定轮询多址协议。该协议根据各节点内分组的当前等待时间及信道状态动态的控制轮询过程,每个轮询周期对具有分组最长等待时间和好的信道状态的节点进行服务。在假设信道为两状态马尔可夫模型的基础上,通过采用嵌入马尔可夫链理论和休假排队模型,给出该协议的理论模型和性能分析,并且通过与基本轮询系统对比分析,可以看出所提出系统缩短了分组的平均等待时间,提高了系统吞吐量。
关 键 词: 中图分类号: 文献标识码: A
(Abstract: Key words:     

流媒体技术发展现状及应用策略综述

随着互联网的普及,网络已经成为人们获取信息的重要渠道,各种各样的多媒体应用层出不穷,但网络带宽却影响着信息传输的速度,因此流媒体技术应运而生,并不断发展,进而得到广泛应用。本文在介绍流媒体技术基本概念的基础上,分析了流媒体技术的基本现状,并提出了相应的策略。     

交织和BCH编码对蓝牙2.0数据传输性能的改善

蓝牙2.0+EDR规范新增DH分组没有有效的纠错机制,其抗干扰能力差。通过在新规范中加入BCH编码和交织编码,以改善蓝牙的数据传输吞吐量及抗干扰能力。对于新增的数据分组,根据蓝牙标准协议,推导了相应的分组特性;建立了GE信道下数据传输速率与信道突发错误水平的关系模型;获得了在不同信道突发错误水平下的数据传输吞吐量。结果表明,在蓝牙2.0+EDR新规范中加入BCH编码和交织编码,在较高突发错误水平的信道中,其数据传输吞吐量提高了一倍以上,明显改善了数据传输的抗干扰能力。     

Beta-Binomial删除信道中的喷泉码文件传输协议

由于命名数据网络(NDN,Named-Data Networking)无环路、逐包、逐跳转发的特点,使得数据包回传成功率降低,而传统的TCP/IP协议中的ARQ和ACK机制对于多播会话不再适用.由于NDN中的传输信道可以等效为二进制删除信道,因此可以通过应用层编码来实现文件的可靠传输.传统的信道编码技术如卷积码、级联码和RS码等复杂度较高,而将NDN与低复杂度的喷泉码的结合可以实现分布式的存储架构,因而可通过喷泉编码在应用层协议中实现可靠的纠删机制,保证整体文件的传输可靠性.以往的研究一般是基于确定的删除概率信道模型,但是由于网络的异构性和信道噪声等因素影响,可能会造成信道丢包概率呈随机性分布.因此,本文在Beta-Binomial分布模型的前提下,根据贝叶斯统计的先验信息和中心极限定理,对随机概率下的纠删信道的文件可靠传输协议进行了数学建模和理论推导.仿真结果显示此模型更具有普适性,此传输协议可在信道状况未知的前提下从理论上求出最小发包数,减少冗余编码包,提高文件整体的投递成功率,在保证传输可靠性的同时有效提升协议传输效率.     

应用于流媒体传输研究的网络流量模拟器

为方便流媒体传输算法的研究，文中提出了利用流量模拟器对网络流量进行控制和调节的方法。从而在实验室内建立一个能够模拟互联网传输参数的实验环境．影响流媒体传输的主要参数为带宽、延时、延时抖动和丢包率，流量模拟器主要对丢包率、延时和带宽等参数进行控制和调节．在模拟实验中，模拟的输出参数基本同预设参数一致，验证了模拟器的可行性．     

流媒体隐蔽通信系统模型及性能优化

针对流媒体载体类型的多样性造成隐藏过程的不一致等问题,提出了一种流媒体隐蔽通信系统的3层模型,该模型将流媒体的隐蔽通信过程划分为适配与执行、传输管理和隐蔽应用3个层次,定义了各层的功能、服务和接口原语等规则.针对隐蔽通信系统中的主要参数建立了数学模型,得到了隐蔽信道有效利用率的表达式,利用求偏导数方法计算出给定条件下系统参数的最佳值.该模型已经在VoIP隐蔽通信系统中得到实现.实验和测试表明:分层模型很好地解决了不同载体下流媒体隐蔽通信隐藏过程的一致性问题,模型的理论计算值对实际系统的优化设计具有直接指导意义.     

一个基于Web Service的流媒体测试系统的设计与实现

流媒体点播是目前流行的一种宽带业务,对网络的丢包率、QoS质量和带宽有特殊的要求,遇到网络阻塞、服务器负载过大时会发生图像停格、声音时断等播放异常。描述了开发一个基于W eb Service的流媒体测试系统的方案。通过建立若干测试点,自动记录各种流媒体参数并上传,可以真实模拟客户的使用场景,方便管理员及时发现并处理问题,具备效率高、成本低和维护方便等特点。     

无线流媒体服务系统的设计与实现

为了满足移动用户对视频服务的需求,设计了无线流媒体系统．该系统采用AVS_M视频标准压缩视频文件,并将压缩文件以3GP文件格式存放于服务器．系统通过RTSP协议控制流媒体播放,SDP协议描述流媒体会话,RTP／RTCP协议传输和控制3GP流媒体数据．在NS2通信系统仿真软件和实验平台测试结果表明, 设计的系统能够更好服务于流媒体传输与终端回放．     

基于Linux平台下实时流媒体传输在远程教育系统中的应用

随着计算机网络的高速发展,促进了远程教育的推广与深入,但是在传输多媒体教学资源时,包括实时数据、网络拥塞、时间等待等问题使得教学效果并不理想,而流媒体技术的应用使得网络教学注入了新的活力。本文阐述了使用流媒体技术传输多媒体教学资源,同时着重介绍了基于Linux平台下的流媒体的传送与接收在远程教学系统中的实现。     

Enhancing Bluetooth 2.1's anti-interference ability based on interleaving coding

The error correction algorithms of Bluetooth are analyzed and improved for the defect of anti-interference ability. To enhance the data transmission throughput and anti-interference ability efficiently, an error correction enhancing mechanism (EECM) combining the forward error correction with interleaving is adopted for Bluetooth, a method of adding the DM packet with an interleaving code to the Bluetooth 2.1+EDR specification is proposed. The mathematical models of the data transmission throughput are set up over the Gillbert-Elliott channel; A numerical simulation of the throughput of different packets in different burst errors are carried out using the model. Simulation results show that adding DM packets and DMI packets to Bluetooth 2.1+EDR specification can improve the anti-interference ability and enhance data transmission throughput significantly in the burst errors channel. Finally, the realized results of the enhanced IP and enhanced Bluetooth baseband IP are obtained by using VLSI design techniques. The performance of the enhanced the Bluetooth baseband is analyzed in comparison with the standard Bluetooth baseband.