Eureka147 DAB的现况（1）

1 前言 在数字广播日益发展的今天,7年前在欧洲开展的Eureka147规划的数字音频广播(DAB)究竟发展到了什么程度?尤其是在欧洲的地面数字电视(DVB-T)开展以后,两者之间出现了什么局面?DAB的前景如何?一直是我国广播界所关注的问题。日本放送技术杂志(2002.10)在这方面有新的报道,现简介如下。     

Eureka-147 DAB近况

本文详细介绍了各国采用Eureka-147 DAB的情况和对其态度；分析了当今世界上几种主要DAB接收机的特点。简单介绍了生产DAB接收机专用芯片的情况，列举了所有参加世界Eureka-147 DAB组织的机构，最后对Eureka-147 DAB的发展趋势进行了总结。     

DAB,是空中泡沫还是"空中客车"

两三年前,DAB有一阵颇为热闹的日子.新老广播,都为这一新生事物侧目,国内有应声立项的开路先锋.DAB颇为时尚,京津唐、上海、广东都有试点.眼下,它的发展情势又如何?不妨走马观花地看看国外的情形.     

DAB（S）,DAB（E）和DAM

本文对ＤＡＢ（Ｓ），ＤＡＢ（Ｅ）和ＤＡＭ三种数字音频广播方式进行讲解和比较，并对数字音频广播的发展提出自己见解。     

DAB同步网技术（上）

在ＤＡＢ（数字音频广播）系统中，可用单一频率构成同步发射网实现大面积覆盖。本文讨论了ＤＡＢ实现单频网（ＳＦＮ）的基础、同步运行的保证、工作频段、网络增益、单频网设计和覆盖空隙的填充技术等有关问题；最后讨论了Ｌ波段ＤＡＢ同步网。     

数字音频广播（DAB）的发展近况

本文介绍了ＤＡＢ的使用频段、尤里卡１４７系统以及美国ＤＡＢ研究动态。     

DAB接收机的两种实现方法

１引言数字音频广播将传统广播的单一声音业务拓展为能同时传递各种诸如图像、文字、数据、图片及活动影像等数字业务，为传统广播业务的发展开辟了广阔的空间。DAB接收机的开发也成为相关技术关注的热点，DAB发送的是数字音频信号及其它各种业务数据，涉及到源编码、数据复用、时间频率交织、纠错编码、正交调制等各种数字信号处理技术，所以DAB接收机要比传统的FM及AM收音机复杂很多。随着TI公司新一代高速DSP的面世，以软件无线电概念实现商用DAB接收已成为可能。随着DSP技术的日益成熟，其快速、低功耗、可编程、实时处理等特…     

Joint synchronization in Eureka 147 DAB system based on abruptphase change detection

We present a joint symbol, frame, and carrier synchronization method for the Eureka 147 DAB signal. Symbol timing is determined first by detecting an abrupt change in the phase angle of the complex product between the last quarter of a useful symbol and its cyclic extension in the guard interval. The detection of this abrupt change is based an the maximal likelihood (hit) principle. Frequency offset of fractional carrier spacing is estimated from the phase angle of the autocorrelation after symbol timing is estimated. Coarse frame synchronization and null symbol detection can also be achieved through this correlation information. Frequency offset of integral carrier spacing is determined from the convolution outputs between a received phase reference symbol and several locally generated but frequency-shifted phase reference symbols. We found the length of a guard interval is the most important parameter for the synchronization algorithm to work. Simulation results show that the performance of this synchronization method approaches to the ideal synchronization case in both an additive white Gaussian noise (AWGN) channel and a two-path Rayleigh fading channel     

L-band DAB Eureka 147 field trials and coverage measurements in urban areas

This paper presents the field trials and the coverage measurements carried out in urban areas in the first experimental terrestrial DAB (T-DAB) network at L-band in Spain. The trials focused on obtaining the parameters that characterize the propagation channel for different urban environments. The results are discussed taking into consideration recommended parameters and values given by international organizations (ITU-R, ETSI) as well as the ones obtained in former experimental networks worldwide.     

The Performance Analysis of Backward Compatible Modulation With Higher Spectrum Efficiency for DAB Eureka 147

Based on the standard of digital audio broadcasting (DAB) Eureka 147 system to improve structures of transmitter/receiver, this paper proposes a physical layer transmission technique capable of boosting the spectrum efficiency up to two times of that of the DAB-Eureka 147 system while the backwards compatibility is guaranteed. The proposed transmission technique comprises the development of both the modulation and demodulation schemes. In the developed modulation scheme, differential 16-level amplitude/ phase shift keying (D16 APSK) is adopted to replace the differential quadrature-phase-shift-keying (DQPSK) used in the DAB Eureka 147 system. In the developed demodulation scheme, on the other hand, a detector for two-level differential amplitude-shift-keying (DASK) signal is proposed which can be implemented with rather low hardware costs. The performance is presented by the Simulink platform in multipath fading channel model.     

数字音频广播（DAB）的发展现状及战略思考（下）

3我国 DAB发展现状我国自 80年代末以来一直跟踪国际上 DAB技术发展动向。1992年 6月 ,原广播电影电视部通过了广播科学研究院完成的在我国开展 DAB重大科研项目的可行性报告 ,并上报国家科委。1994年 12月 ,国家科委通过了广播电影电视部起草的《数字音频广播(DAB)重大科技产业工程可行性论证报告》。1996年 5月 13日 ,国家科委在京召开了“国家重大科技产业工程数字音频广播(DAB)实施方案”专家综合评审会 ,通过了“实施方案”,12月 11日正式将此项目列入“九五”国家重大科技产业工程计划。该项目主要有三个目标 :(1)制订我国DAB…     

数字音频广播(DAB)的发展现状及战略思考(上)

20 0 2年 1月 15日 ,广电总局下发关于“2 0 0 2年广播影视工作要点”的文件 (广发办字[2 0 0 2 ]2 3号 ) ,其中第 2 8条的主要内容为 :“加强数字声音广播的跟踪研究和发展战略研究 ,提出发展我国地面数字声音广播、卫星数字声音广播、数字调幅广播的对策与政策建议 ,研究制定数字声音广播的技术体制、标准、发展规划和过渡方案。”这一决策的发布标志着我国声音广播的数字化进程即将正式启动 ,沉寂多年的数字音频广播 (DAB )将再度成为广播影视科技工作的热点。本刊将分两期连载广科院战略规划所提供的专题研究报告———数字声音广播(DAB )的发展现状及战略思考 ,相信对关注我国数字声音广播发展的业界人士不无启迪     

The use of big LEO satellite systems and EUREKA 147 DAB to providereliable BC reception

A LEO broadcasting satellite system for EUREKA 147-DAB is discussed and analyzed. It can provide a continuous, worldwide service, which is not interrupted by satellite handovers. A complete S-DAB service is provided by overlapping cellular service areas. Each cell may have an individual uplink station without any sophisticated components. The system analysis indicates that the link margin of the proposed system can overcome the problems of blockage and foliage attenuation, which are significant in the alternative GEO/HEO systems. The analysis also reveals that the specifications of the EUREKA DAB COFDM signal are adequate to cope with range and range rate effects due to the satellite motion. The system concept is based on the exploitation of range, range rate, and angular information onboard the satellites with respect to each individual uplink station in order to compensate for Doppler frequency shifts and for variable signal propagation delay     

光伏发电系统并网控制技术现状与发展(下)

由于LCL滤波器针对高频谐波的滤除效果优于L型滤波器,因而广泛应用于电流源控制型的光伏并网逆变电路中,但也导致了基于LCL滤波器的光伏并网逆变器控制策略更为复杂,因此本文并从并网控制策略角度分析了间接电流控制与直接电流控制两种并网策略,并预测了未来光伏发电系统并网控制策略的发展趋势。     

传声器(二)

３传声器的选用目前市场流行品牌有AUDIX（奥迪克斯）、AKG、SHURE（舒尔）、beyerdynamic（拜亚动力）、SONY（索尼）等等。根据不同的使用用途，可适当选择合适的厂家和型号。（１）AUDIX专业演唱传声器（巡回演唱）———OM系列OM系列传声器（如图７所示）最适合演唱会。OM系列具有７种型号，从OM－１到OM－７，它们分别适用于不同的演出场所。在此只介绍OM－６，该传声器是全频传声器，能够在６３Hz的音频下将声音完美再现。声音纯净，更具录音棚效果，又因其低染色而倍受音乐家喜爱。（２）AUDIX乐器拾音传声器———…     

数字音频广播DAB

简述了数字音频广播DAB及其采用的创新技术，如MUSICAM编码方法，CDFDM传输方式以及DAB的不同与传统音频广播的覆盖方式和数字化大潮中广阔的发展前景及对未来音频广播发射和接收的深远影响。