VoIP技术及其应用

文章叙述了语音在互联网络上传输VoIP(Voice over IP network)的关键技术、国际标准以及VoIP的应用和发展状况.文章对VoIP的技术体系结构进行了的详细阐述,重点介绍了语音在IP网络上传输时的技术难题和保证VoIP语音通讯质量QoS(Quality of Service)的关键技术.     

IP核心网中VoIP业务服务质量的初步研究

通过对比传统电话网的语音业务特点对IP核心网中的VoIP业务流进行了模拟,并通过仿真对IP核心网中VoIP业务流特性进行了观察分析。结果发现,大量VoIP业务汇聚产生的业务流具有突发性小、较平稳的流量特性,因而不必为其分配过多的带宽资源;研究了Internet自相似业务流特性对VoIP业务性能的影响,提出了在VoIP业务中采用高优先调度机制等技术来保障VoIP服务质量的网络设计原则。     

VoIP技术、标准及应用

本文综合叙述了语音在互联网络上传输(VoIP)的关键技术、相关的国际标准、应用前景及目前研究的进展状况.着重阐述了VoIP中的语音压缩,网络通讯协议,服务质量保证(QoS)等相关的实现技术和标准.最后介绍了中国科学院东海研究站在VoIP研究方面的进展状况.     

VoIP技术及其应用

文章叙述了语音在互联网络上传输VoIP(Voice over IP network)的关键技术、国际标准以及VoIP的应用和发展状况。文章对VoIP的技术体系结构进行了详细阐述，重点介绍了语音在IP网络上传输时的技术难题和保证VoIP语音通讯质量QoS(Quality of Service)的关键技术。     

COFDM应急通信指挥系统及应用

COFDM编码多载波正交频分复用数字调制技术,提高了传输抗干扰能力,结合超短波"绕射"穿透"特性,很大程度上克服了微波、卫星移动传输过程需要天线伺服的问题,特别适用于不确定灾害环境的应急组网。可以解决现场到指挥车、指挥中心图像语音的实时传输,并且安装到车辆、船舶、直升机/无人机等移动平台上,组成灾害现场各种应急通信指挥网。     

一种抗RPE-LTP声码器压缩的端到端数据传输方法

提出了一种基于正交频分复用（OFDM）的抗规则脉冲激励-长时预测声码器（RPE—LTP）压缩的端到端数据传输方法。根据RPE—LTP声码器特性,将待传输数据分别调制到正交的低频正弦载波上,用快速傅立叶逆变换运算实现信号的调制传输,调制后的波形符合声码器的时频特性。经仿真结果验证,提出的抗压缩传输方法的数据传输速率可达2．4kb／s,误码率小于0．3％,适合移动网络端到端实时安全语音数据传输使用。     

浅谈电力调度数据网的传输特性

在电力系统的运行发展中,电力调度数据网是极其重要的组成部分,它所承载的信息交互任务,是保证电力系统调度运行安全的基础。本文在建立电力调度数据网数据传输模型的基础上,深刻探讨了电力调度数据网在传输中的特性,并得出以下分析结论:电力调度数据网的传输特性与拓扑结构有着密切联系,星型网络比网状网络更具传输性能,如果在出现攻击之后,星型网络与网状网络的传输特性会呈现出恶化现象,其中以网状网络最为严重。     

基于正交复小波变换和小波去噪的改进系统De-OCWDM

用近似线性相位正交复小波变换(ALOCWT)取代了正交频分复用(OFDM)系统中的离散傅立叶变换(DFT),形成了正交复小波波分复用(OCWDM)系统.ALOCWT具有时频特性、正交特性、重构特性等特性,能够很好地取代DFT,同时ALOCWT能够保留复信号的相位信息,使得信号重构精度更高,从而提高了信号传输的准确性和系...     

基于TCP的实时流媒体传输性能分析

针对下一代网络中多媒体信息的网络传输方式正从UDP向TCP回归,研究了基于TCP的实时流媒体传输方法的性能.结合TCP快重传、快恢复的特性和拥塞窗口的变化规律,从微观角度分析了TCP播放缓冲区对流媒体播放质量的影响,通过进一步分析语音流的组帧传输与视频流的分帧传输过程,推导证明了在Internet上使用TCP传输实时音...     

基于熵的语音音质评价方法

研究一种基于熵的语音音质客观评价方法,解决语音编、解码,通信设备研制以及通信干扰性能判定过程中长期使用主观评价的不便性。首先详细分析了信息的统计特性,在此基础上引入了马尔可夫信源并论证了语音信号的马尔可夫特性,介绍了一种用马尔可夫熵来表征语音音质变化的方法,试验数据验证了该方法具有一定的可靠性、可行性和应用前景。     

Dual power-saving modes for voice over IP traffic supporting voice activity detection

In the context of the IEEE 802.16e standard, a dual power-saving mode (DPSM) algorithm for voice over IP (VoIP) traffic whose voice codec supports voice activity detection is proposed. The proposed algorithm utilises the inactivity of the voice codec of each conversing party during mutual silence periods. Using the suggested method, the length of the sleep intervals varies during mutual silence periods, while during talk-spurt periods it is fixed according the VoIP packet generation ratio. The performance of the proposed DPSM algorithm for the average packet-buffering delay in the base station (BS) and the energy consumption of a mobile station (MS) is evaluated numerically and validated with the aid of computer simulation. The results show that when the proposed combined method is used, the energy consumption of an MS is considerably less when a PSM that only uses sleep intervals of a fixed length is operating. This improvement in performance comes at the cost of greater packet-buffering delay in the BS.     

基于统计性QoS保证的数据包延时界调度算法

讨论了调度算法的性能指标，对目前基于业务流的调度算法的技术特点与性能优劣进行了分析和比较．重点研究了基于时延和丢包率的算法，并提出了一种基于数据包延时界（PDB）排列的调度策略，与WFQ及传统EDF算法进行了比较，证明业务端到端超时概率随网络带宽利用率的变化性能优于传统EDF算法．     

Finite capacity scheduling with mixed duration tooling trees

Finite capacity scheduling is a research area which has much practical application and the quality of the schedules has a major impact on the delivery performance, profitiability and finance requirements of companies. This paper proposes a method of finite capacity scheduling where activities have a range of mandatory and alternative tools which can be used, and some of the less preferred tools run at a slower rate. The calculations are presented by example, and in the context of a computer program to implement the algorithms.     

Survey and Analysis of VoIP Frame Aggregation Methods over A-MSDU IEEE 802.11n Wireless Networks

The IEEE 802.11n standard has provided prominent features that greatly contribute to ubiquitous wireless networks. Over the last ten years, voice over IP (VoIP) has become widespread around the globe owing to its low-cost or even free call rate. The combination of these technologies (VoIP and wireless) has become desirable and inevitable for organizations. However, VoIP faces a bandwidth utilization issue when working with 802.11 wireless networks. The bandwidth utilization is inefficient on the grounds that (i) 80 bytes of 802.11/RTP/UDP/IP header is appended to 10–730 bytes of VoIP payload and (ii) 765 µs waiting intervals follow each 802.11 VoIP frame. Without considering the quality requirements of a VoIP call, be including frame aggregation in the IEEE 802.11n standard has been suggested as a solution for the bandwidth utilization issue. Consequently, several aggregation methods have been proposed to handle the quality requirements of VoIP calls when carried over an IEEE 802.11n wireless network. In this survey, we analyze the existing aggregation methods of VoIP over the A-MSDU IEEE 802.11n wireless standard. The survey provides researchers with a detailed analysis of the bandwidth utilization issue concerning the A-MSDU 802.11n standard, discussion of the main approaches of frame aggregation methods and existing aggregation methods, elaboration of the impact of frame aggregation methods on network performance and VoIP call quality, and suggestion of new areas to be investigated in conjunction with frame aggregation. The survey contributes by offering guidelines to design an appropriate, reliable, and robust aggregation method of VoIP over 802.11n standard.     

OFDMA系统中资源公平调度算法研究

研究了宽带正交频分复用多址（OFDMA）系统中存在多种不同业务时的无线资源公平调度问题,深 入分析了经典的资源调度算法———用户最小容量最大化算法,提出了一种明显改善公平性能的改进算法,仿真 结果证明,改进算法在各种应用环境下,都具有良好的公平性能,能为不同业务类型的用户提供较严格的速率 保证。     

基于Monte Carlo指数平滑订单预测与决策分析

目的为了解决电商企业订单到达的不确定性和仓储运营的特殊性造成的人员配置不合理问题,提出一种构建基于订单预测和产线平衡为目标的Monte Carlo季节指数平滑和作业产能模型。方法应用概率统计方法解决信息不完全下订单预测问题。通过该方法对季节指数平滑法中的平滑系数进行优化,以修正预测模型,然后用Crystal ball软件对预测值进行产线调度优化。结果算例分析表明,使用该方法进行预测时,精度提高了45%,并将预测值用于拣选作业产能安排,确定了最优人员数量和工时分配方案。结论可以为电商类企业提供准确的订单预测信息,以及合理的作业人员配置方案,提高了企业的运行效率。     

共享策略下甩挂车辆调度问题的分析及求解

目的为了克服现阶段下甩挂货运过程中存在的空载率高、牵引车利用率低等问题,从服务点间的货运关系出发,对货运单循环系统中共享策略下甩挂车辆调度问题进行设计研究。方法以牵引车行驶总里程为目标函数,构建共享策略下甩挂车辆调度模型,并基于模拟退火算法对其进行优化求解。结果以山东省的2家小型运输企业为案例进行了仿真分析,与普通车辆调度模式分析比较可知,共享策略下调度模式的空载率、单位货运成本、单位货运油耗、牵引车利用率分别优化了79.6%,50%,22.6%,171.4%。结论文中构建的共享策略下甩挂车辆调度模型及其求解算法可行有效,在减少空载行程、提高燃油利用率等方面具有良好的效果。     

基于规则和仿真的多机并行作业车间生产调度研究

资源分派和能力分派是作业车间生产调度中的重要问题,路径选择规则和分派规则是解决上述问题的有效途径。采用基于规则的仿真研究多机并行作业车间资源分派和能力分派问题,分析工件加工时间、到达率以及机器加工速率对调度结果的影响,以平均完工时间、平均延迟交货率以及平均资源利用率为评价指标,通过对4种路径选择规则和6种分派规则的仿真试验,确定不同性能指标下最佳的调度规则。仿真研究表明:调度规则的选用取决于车间资源配置和调度目标,应避免仅凭借经验或偏好选择规则的调度方法。     

Uncertainty Evaluation of Objective Speech Quality Measurement in VoIP Systems

This paper deals with the measurement uncertainty of the speech quality (SQ) achievable by an actual Voice-over-Internet-Protocol (VoIP) telephony network. The accuracy of end-to-end speech data provided by the Perceptual Estimation of SQ (PESQ) algorithm suggested in the International Telecommunication Union (ITU) recommendation P.862 is discussed. Then, the uncertainty of the PESQ results under different measurement conditions and real-life VoIP equipment (Media Gateway) is analyzed. This problem, in fact, has received very little attention in the literature, although many results related to other kinds of PESQ applications are available. Meaningful experimental data are reported and discussed mainly by means of statistical tools.      

A logistics scheduling model: scheduling and transshipment for two processing centers

Logistics scheduling refers to problems in which decisions on job scheduling and transportation are integrated into a single framework. A logistics scheduling model for two processing centers that are located in different cities is presented. Each processing center has its own customers. When the demand in one processing center exceeds its processing capacity, it is possible to use part of the capacity of the other processing center subject to a job transshipment delay. Such a coordinated scheduling situation can be modeled as a parallel-machine scheduling problem with transshipment between the machines. We study problems with different objective functions and constraints, and propose various algorithms to solve these problems. Discussions on the benefits and incentives for the coordinated approach are presented.