Standardization on performance objectives of satellite systems using adaptive coding and modulation

The radiocommunication part of the International Telecommunication Union (ITU‐R) establishes the standards for wireless communications. Recommendation ITU‐R S.1062 specifies the performance objectives for satellite communication systems providing constant bit rate service. However, this is not applicable to most modern satellite communication systems utilizing adaptive coding and modulation (ACM) schemes to compensate for channel impairments, especially for systems operating in high frequency bands. For this reason, ITU‐R recently developed Recommendation ITU‐R S.2131 that is suitable for satellite systems with ACM. The developed Recommendation provides a method to determine performance objectives for satellite systems using ACM. Two possible objective parameters are presented, including packet error rate and spectral efficiency. This paper presents the standardization process, and the background used to establish new performance objectives. In addition, interpretations of the objectives are given by using estimation results for two different propagation characteristics.     

国际电联WRC-23大会移动通信频率有关新议项浅析

国际电信联盟(ITU)2019年世界无线电通信大会(WRC-19)为2023年的下届大会明确了新的研究议项,其中有若干个针对国际移动通信系统(IMT)频率规划有关的议项,频段主要聚焦在约10 GHz以下的中、低频段.文章对这些议项的背景、主要内容进行介绍,对其中的主要问题和工作方式开展分析,并对后续工作提出思考.     

A Perceptually Motivated Active Noise Control Design and Its Psychoacoustic Analysis

The active noise control (ANC) technique attenuates acoustic noise in a flexible and effective way. Traditional ANC design aims to minimize the residual noise energy, which is indiscriminative in the frequency domain. However, human hearing perception exhibits selective sensitivity for different frequency ranges. In this paper, we aim to improve the noise attenuation performance in perceptual perspective by incorporating noise weighting into ANC design. We also introduce psychoacoustic analysis to evaluate the sound quality of the residual noise by using a predictive pleasantness model, which combines four psychoacoustic parameters: loudness, sharpness, roughness, and tonality. Simulations on synthetic random noise and realistic noise show that our method improves the sound quality and that ITU‐R 468 noise weighting even performs better than A‐weighting.     

Modified rain attenuation model for tropical regions for Ku‐Band signals

Attenuation measurement on Ku‐ band satellite signal in a tropical site, Fiji is presented. Rain‐attenuation prediction by ITU‐R and the Crane Global models showed noticeable deviation to the measured values. Unlike the monotonic decrease predicted by these models, exceedance of rain‐rate and attenuation in Fiji and other tropical regions showed the presence of breakpoints. For Suva, the breakpoint in rain‐rate and attenuation were at 58 mm/h and 9.4 dB with exceedances of 0.009 and 0.018%, respectively. Modifications to the ITU‐R model are proposed in this paper, for adopting it in the tropics. These modifications are based on the properties that in the tropics (i) the accumulation time factor at the breakpoints is an invariant (ii) for elevation angles <60° and at high rain rates multiple rain cells intersect the slant path. The attenuation exceedance is predicted by two expressions similar to the ITU‐R model, one for rain‐rates lower than the breakpoint rain‐rate and the other above it. The modified prediction model show remarkable agreement with the measured Ku‐band attenuation in seven tropical sites. Copyright © 2006 John Wiley & Sons, Ltd.     

数字视频压缩编码的国际标准

系统地分析了H.26x,MPEG-1,MPEG-2,MPEG-4,MPEG-7等视频压缩编码国际标准的特点和性能，并说明了它们的应用领域和发展现状。     

我国电信标准化的发展及有关建议

电信网在支持越来越广泛业务要求的同时，要实现降低网络成本，提高网络效率，共享网络资源的目标，根本保证是电信网的标准化。作者扼要介绍了我国在加强电信标准化，促进通信网络发展方面取得的长足进步，并提出对今后进一步加强电信标准化工作的几点建议。     

ITU内部知识产权披露管理分析

2009年5月，ITU对知识产权披露流程进行了新的规范，以提高ITU中知识产权数据库中数据的准确性和有效性，文章在对ITU披露原则分析的基础上，指出了原有的披露管理流程的缺陷，并对此次修改过的流程管理进行了深入的分析，希望能够给中国通信企业以参考，深入了解披露专利的含义，并能有效应对。     

基于FPGA的多路图像采集系统的软件设计

分析了现有的视频采集方案的研究现状,对如何采用CCD摄像头采集多通道、高分辨率、高质量的图像以及基于FPGA的嵌入式图像采集系统的实现方法做了研究。与传统图像采集系统相比,该系统主要利用四片视频解码芯片SAA7113H和两片FPGA完成对四路图像的同时采集、存储和显示,能根据FPGA里UART模块接收到的指令切换一路图像在LCD或是VGA上全屏显示。实现了对两个FPGA的级联配置,针对视频解码芯片ADV7181B,实现了I2C总线配置、ITU656解码以及数据格式的转换。并根据多次实验,对最终显示图像的抖动现象作了分析和提出解决方法。结果证明,该系统具有低成本、高可靠、灵活性好等特点。     

ITU的组织机构和成员权利

本详细介绍了ITU的发展历史、组织机构和成员权利。     

低比特率语声编码器的新发展

ITU-T建议G.729、G.729 AnnexA和G.723.1是国际电信联盟(ITU)最新颁布的3种适用于多媒体通信的低比特率线性预测语声编码器标准。文章介绍了语声编码器的比特率、复杂度、延迟和音质等性能指标的含义,并通过比较3种标准的新型声码器在算法和性能指标上的异同点,讨论了它们在多媒体通信中的不同应用。