ITU—T G．652、G．655、G．657单模光纤标准的解析

介绍和解析了ITU—T最近十年来先后发布的G．652、G．655、G．657单模光纤各个制定和修订版本,对其主要技术要求及演变趋势进行了比较和分析。简述了近期光纤制造技术的发展状况,最后提出了两点建议。     

G．729A在语音网关（VoIP）中的应用

随着VoIP(Voice over IP)技术的快速发展,VoIP语音网关成为语音通信中一个十分重要的设备.由于在语音网关中涉及复杂的语音信号处理,同时目前VoIP的标准正处于不断完善之中,因此采用可编程DSP(Digital signal Processor)芯片来实现语音网关中语音压缩编解码模块是一种有效的解决方案,用户可以很容易地升级软件代码.使用TI公司的DSP开发板(嗍20C5416芯片)设计和实现的语音网关中G.729A编解码模块,从算法实现的复杂度、占用的存储空间和实现的话音合成质量方面都达到了实用的要求,且各项性能相当优越.     

一种新型的G.652和G.655光纤混合光缆

介绍了一种全新结构的G.652和G.655光纤混合光缆,它很好地满足了长途骨干网对G.655光纤传输指标方面的高要求和城域网对G.652光纤可操作性方面的要求,是一基于应用设计光缆的实例。     

一种G.729ab和G.723.1联合多通道声码器设计

以TMS320C6203为硬件平台,设计了一种高效率的G.729ab和G.723.1联合多通道声码器.该声码器的不同通道可同时实现G.729ab和G.723.1两种语音压缩算法.通过使用纯汇编指令与C语言结合优化编程,提高核心编解码算法效率,可实时最大支持31个话路语音的G.729ab编解码,或22个话路语音的G.723.1编解码.利用TMS320C6203在片外设McBSP提供声码器连接PSFN的标准E1接口;利用TMS320C6203的HPI接口提供声码器和连接数据网的RTP协议接口,使该联合声码器可灵活应用于媒体网关.     

ITU-T新G.657标准与G.657.B3光纤

本文在对ITU-T G.657最新标准进行解读的基础上,简单介绍了长飞公司G.657.B3光纤EasyBandUltra;并根据G.657.B3光纤具体的应用环境,从客户使用的角度,初步探讨了评判G.657.B3光纤性能优劣的几个关键参数。     

Walter R. G. Baker

The IRE awarded its 1952 Medal of Honor to Walter R. G. Baker for "his outstanding direction of scientific and engineering projects" and "his statesmanship in reconciling conflicting viewpoints and obtaining cooperative effort."     

ITU-T G.711.1: Extending G.711 to Higher-Quality Wideband Speech

In March 2008 the ITU-T approved a new wideband speech codec called ITU-T G.711.1. This Recommendation extends G.711, the most widely deployed speech codec, to 7 kHz audio bandwidth and is optimized for voice over IP applications. The most important feature of this codec is that the G.711.1 bitstream can be transcoded into a G.711 bitstream by simple truncation. G.711.1 operates at 64, 80, and 96 kb/s, and is designed to achieve very short delay and low complexity. ITU-T evaluation results show that the codec fulfils all the requirements defined in the terms of reference. This article presents the codec requirements and design constraints, describes how standardization was conducted, and reports on the codec performance and its initial deployment.     

Biography - A. G. Clavier

A. G. Clavier was born in France in 1894. He graduated at the Sorbonne as "Licencie en Sciences Physiques et Mathématiques" and received the diploma of Electrical Engineer from the Ecole Superieure d' Electricité (Paris) in 1920. He started his career of radio research as the head of one of the Laboratories of the French Signal Corps, in charge of military developments in the higher part of the radio-frequency spectrum. He was a member of the French jury supervising the famous amateur contest in 1923 for short-wave transatlantic qomrnunication. He was Secretary of the Redaction of "Onde Electrique" during its first years of existence (1922-1925).     

Comments on `Orthogonality of exponential transients' by G.R.L.Sohie and G.N. Maracas

The work of Sohie and Maracas (ibid., vol.86, no.12, p.1616-18, Dec. 1988) concerned the representation of a decaying time function by a weighted sum of exponentials. It is shown that the problem can be solved in greater generality and in a more straightforward manner by using classical vector-space methods. The classical vector-space analysis is specialized to a particular function space containing the exponential transients     

G.729标准与G.723.1标准编码方法区别的研究

介绍了G．729，G．723．1两种语音编码标准的主要用途和它们各自使用的算法。并就两种标准的编码算法的码率、线性预测分析、延时以及编码方法等几个方面进行了比较。在线性预测分析时主要是对两种算法在加窗时的不同进行了陈述；在编码方法的比较中又涉及到预处理时由于使用的高通滤波器的差别而导致G．729编码话音质量优于G．723．1的原因。     

基于G.729A和G.729D的宽带语音编码实现

根据7kHz声频编码标准G.722,采用正交镜像滤波器(Quadrature Mirror Fihers,QMF)法将宽带语音划分为等频带的子带,而后采用高质量的语音编码标准G．729,对低频带使用简化的G．729A,高频带使用较低比特的G．729D,实现了低时延的14．4Kb／s的宽带语音编码。