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Digital Audio BroadcastingThe description of DAB technology is from the EUREKA 147 project, a cooperative arrangement to develop DAB by the European Broadcasting Union and electronics companies. Although there may be further developments of the technology and, therefore, contenders in the future DAB market, the EUREKA 147 is thus far the only system which has been successfully demonstrated. It is also most certainly the basis for the discussion by the various players in the current policy debate. Sound quality: the sound to noise ratio for DAB will be 90dB compared to 70dB for FM radio. Frequency response for DAB will equal that of CDs at 20Hz to 20kHz compared to the relatively limited range of FM radio at 50Hz to 16kHz.Spectrum efficiency: By using only the sounds that are audible and by eliminating noise allows the signal to be reduced by about 8O7o. The EUREKA 147 system can transmit 16 separate stereo channels in 4MHZ of spectrum.Economically efficiency: Because the signals are interleaved, the transmission facilities would be operated by a consortium for the construction, operation, and maintenance of a common transmission plant. Electrical power conservation and savings also will be a formidable advantage of DAB. Tests of the EUREKA 147 system show that DAB uses at least one-twentieth (some say as high as one-thousandth) the electrical power used by a conventional FM transmitter to cover an equal area.Faithfulness of signal reproduction: DAB receivers will be designed to use reflected signals as alternative sources of information when the primary signal deteriorates. Using smart receivers which correct the fading and interference problems associated with AM and FM broadcasts.Parity among stations and less regulation: Following a complete station migration to a single DAB band, the current distinctions between FM and AM would disappear. Competition between stations could be based on programming rather than technical abilities and advantages. Moreover, technological parity may remove the burden of the technical aspects of radio regulation from the FCCs workload.DAB, as a digitized broadcast radio signal, promises CD quality sound; transmission diversity as either terrestrial or satellite services; signal, spectrum, and economic efficiency; and station parity and less regulation. Of these promises, transmission diversity and station parity are seemingly the most problematic to the currently constricted doctrine of localism.Transmission Diversity: The Question of Satellite DABThe most heated debate to date concerns the effect that DAB will have on the current radio service environment. The word localism is invoked unsparingly in the debate. Those who believe that DAB is a threat to current conditions are primarily concerned with the effects of satellite, superstation DAB services on the advertising base and program content of local radio (i.e., overemphasis of particular formats).The National Association of Broadcasters (NAB), Westinghouse, Pulitzer, Sconnix, and the Tribune Companies (FCC, 1991b) argue that satellite-based DAB services are the greatest threat to localism. All are in agreement that the FCC should ensure the retention of the current level of localism in American radio. The NAB, in arguing that FCC policy should minimize the economic impact of DAB, maintains that satellite DAB would:Affect the amount of advertising placed on local radio stations, and the related cost of air time on the stations rate card. Due to the inherent nonlocal nature of satellite-distributed services, if commercial satellite audio broadcasting services were to be based on advertising, rather than on subscription fees, a substantial percentage of the revenues would likely come from existing national and/or regional advertisers. Consequently, the existing foundations of advertising revenues, supporting local radio services, would be affected, perhaps significantly. (FCC, 1990c).The NAB estimates an immediate loss of revenues at about one fifth of the total economic base of the entire U.S. radio industry, with the heaviest losses felt by AM radio. This figure is based on the total revenues currently received by radio from national and regional advertising, which could possibly shift to satellite based, super-station services, if and when established. They estimate that financial profits for the entire radio industry would drop to zero if less than a third of radios present national/ regional advertising were diverted to satellite-delivered services (FCC, 1990c, p. 15).Of course, all of the arguments made for the maintenance of a terrestrial-only system argue for a market value construct of localism. It is to the advantage of the established broadcasters to support the traditional market construct of localism for economic, as well as political reasons. Economically, they protect their own businesses and market stability.Politically, by supporting the FCCs traditions, the broadcasters confirm the institutional memory of the FCC and their shared past. These conditions support the notion of “FCC as licenser and political protector of the business.”Indeed, stations (and their right to make money) should be ensured by the FCC in exchange for servicing the local area. IntroductionThe new digital radio system DAB (Digital Audio Broadcasting, nowadays often called Digital Radio) is a very innovative and universal multimedia broadcast system which will replace the existing AM and FM audio broadcast services in many parts of the world in the future. It was developed in the 1990s by the Eureka147/DAB project. DAB is very well suited for mobile reception and provides very high robustness against multipath reception. It allows use of single frequency networks (SFNs) for high frequency efficiency.Besides high-quality digital audio services (mono , two-channel or multichannel stereophonic ), DAB is able to transmit programme-associated data and a multiplex of other data services (e.g. travel and traffic information, still and moving pictures, etc.). A dynamic multiplex management on the network side opens up possibilities for flexible programming .In several countries in Europe and overseas broadcast organizations , network providers and receiver manufacturers are going to implement digital broadcasting services using the DAB system in pilot projects and public services . DAB works very differently from conventional broadcasting systems. Most of the system components such as perceptual audio coding ,channel coding and modulation , multiplex management or data transmission protocols are new solutions and typically not so familiar to the expert in existing analogue or digital broadcast systems.System Concept2.1 The Physical ChannelMobile reception without disturbance was the basic requirement for the developmentof the DAB system.The special problems of mobile reception are caused by multipath propagation: the electromagnetic wave will be scattered, diffracted, reflected and reaches the antenna in various ways as an incoherent superposition of many signals with different travel times. This leads to an interference pattern that depends on the frequency and the location or for a mobile receiver the time. The mobile receiver moves through an interference pattern that changes within microseconds and that varies over the transmission bandwidth. One says that the mobile radio channel is characterised by time variance and frequency selectivity.The time variance is determined by the vehicle speed n and the wave length c/f0, where f0 is the transmission frequency and c the velocity of light. The relevantphysical quantity is the maximum Doppler frequency shift:Table 2.1 shows some practically relevant figures for fDmax.The actual Doppler shift of a wave with angle a relative to the vector of the speedof the vehicle is given byAudio Services and Applications3.1 GeneralThe DAB system is designed to provide radio services and additional data services. This chapter focuses on the main audio services as the central application. The audio services use MPEG Audio Layer II to provide mono, stereo and multichannel programmes to the listener. Although the first broadcast applications and receivers will only supply stereo programmes, the migration to multichannel services is nevertheless already included in the system.Data services will become more and more important and one can currently see many new ideas on their use being developed and tested. Most advanced is the Internet, but it is easy to envisage that the data capacity of the DAB system can be used for very similar services. This chapter focuses on the main service of DAB the audio broadcasting service and the standard that is being used. We intend to give the reader an understanding of the features of the audio system and the possible pitfalls without going into too many details that the user (content provider, broadcaster and listener) has no influence on.Data Services and Applications4.1 GeneralWhile DAB development started mainly focused on audio broadcast, data capabilities have been designed into the system right from the beginning. After successful presentations of the new digital audio broadcast system at the beginning of the 1990s, these data capabilities gained more and more interest and prototype data services were demonstrated by different project partners of Eureka 147 at related events (e.g. at NAB in Las Vegas, Spring 1992). In order to harmonise these prototype data services and to reach compatibility between the equipment and services, data interfaces, protocols and applications were defined to match the needs of broadcasters, service providers and end users. In the meantime it is generally accepted that the usage of some DAB channel capacity, Especially for multimedia data services, is crucial both for user acceptance and for financing of the networks of this new digital broadcast medium. All the necessary hooks are available to follow this route.4.2 Data Service SignallingThe DAB multiplex is organised into services and service components . Data transmissions can either be a service component of an audio service, e.g. if it carries data which are related to the service, or if there is no relation to a programme service, a data service can be transmitted as a standalone service, and can be made up from one or several data service components.References:1Edited by Wolfgang Hoeg/Thomas Lauterbach Digital Audio Broadcasting(principles and applications of digital radio) 20032ETI 300 401 ETS 300 401 Radio broadcasting systems Digital Audio Broadcasting DAB to mobile portable and fixed receivers May 1997数 字 音 频 广 播数 字 音 频 广 播 技 术 的 描 述 来 自 于 EUREKA 147 系 统 ， 由 欧 洲 广 播 联 盟和 各 电 子 公 司 合 作 发 展 数 字 音 频 广 播 。 虽 然 该 技 术 可 能 有 更 进 一 步 的 发 展 ， 但是 在 竞 争 激 烈 的 未 来 数 字 音 频 广 播 市 场 上 ， EUREKA 147 系 统 已 经 被 成 功 的 证明 是 唯 一 久 远 的 系 统 标 准 。 而 这 无 疑 也 是 争 论 当 前 政 策 的 各 方 面 人 的 讨 论 基 础 。声音质量：数字音频广播的信噪比为 90dB 明显优于模拟调频广播的信噪比 70dB。而数字音频广播的频率响应范围从 20Hz 到 20kHz 将可以与 CD 机相媲美，相比较之下模拟调频广播的范围相对较局限从 50Hz 到 16kHz。频谱利用率：在只使用可听得见的声音频率和在允许程度上消除噪声后，信号大约被减弱了 80%。EUREKA 147 系统在 4MHz 的频谱内可传输 16 个独立的立体声频道。经济效率：因为信号是“隔行扫描的” ，传输设备将被一个使其产构造、运算和维护的公共设备的协会操作。电力能源的保存和节约也将是数字音频广播的一个巨大优势。E UREKA 147 系 统 的 测 试 显 示 ， 发 射 覆 盖 相 同 的 区 域 的 信 号数 字 音 频 广 播 发 射 机 所 需 要 的 电 力 是 传 统 的 模 拟 调 频 广 播 发 射 机 所 消 耗 电 力 的二 十 分 之 一 （ 也 有 的 说 高 达 一 千 分 之 一 ） 。信号转发的准确性：数字音频广播接收机将被设计为当主要信号恶化衰减时，可接收使用有选择性来源的转发信号的信息。使用此智能接收机改良了之前模拟调幅广播和模拟调频广播信号容易衰减和受干扰的问题。基站和较少规章之间的对等性：在独立的数字音频广播频段发射基站移植建设完善后，当前与模拟调频及调幅广播的差别将消失。其基站的竞争重点将放在规划设计上更甚于技术水平和优势上。此外，科技上的对等性可以把无线电技术表面的调整工作量负担从美国通信委员会卸下。数字音频广播，作为一个数字化广播无线电信号，承诺有着可与 CD 媲美的音质；其传输方式可以是地面或人造卫星等任一种方式，信号，频谱和经济的效率，地位的对等性和较少的规章。这些承诺中，传输方式的差异和基站对等性对通常有狭隘地方观念的教条学说来说是最明显有疑问的部分。传输差异：人造卫星发射数字音频广播的一些问题当前所关注讨论最热烈的是数字音频广播将对当前的广播服务环境造成什么样的影响。 “地方主义”这个词在讨论中被保守的调用。那些相信数字音频广播对当前的广播环境是一种威胁的人主要是质疑人造卫星的效果， “超级站”数字音频广播服务的广告基础和局部广播的节目内容（也就是说，过分的强调细节形式） 。全 国 广 播 工 作 者 协 会 （ 美 国 ， NAB） ， 韦 斯 汀 豪 斯 , 普 利 策 , 斯 考 尼 克 斯 和论 坛 公 司 (美 国 通 信 委 员 会 , 1991b)争 论 说 基 于 人 造 卫 星 的 数 字 音 频 广 播 服 务对 地 方 主 义 观 念 是 最 大 的 威 胁 。 所 有 人 都 一 致 认 为 美 国 通 信 委 员 会 应 该 确 保 当前 地 方 主 义 在 美 国 无 线 电 广 播 标 准 的 保 持 力 。 全 国 广 播 工 作 者 协 会 ， 在 讨 论 说服 美 国 通 信 委 员 会 的 政 策 应 当 是 要 将 数 字 音 频 广 播 经 济 上 的 冲 突 和 影 响 最 小 化 ，要 使 人 造 卫 星 发 射 的 数 字 音 频 广 播 得 以 维 持 应 该 ：抢 占 大 量 地 方 广 播 的 广 告 市 场 和 那 些 有 关 系 的 在 电 视 节 目 开 始 之 前 的 时 间 段的 站 的 卡 片 比 率 成 本 。 由 于 人 造 卫 星 分 区 服 务 固 有 的 非 局 部 地 区 的 本 性 ， 商 业 的人 造 卫 星 音 频 广 播 服 务是主要是基于广告收入来维持，更甚于签署协议定金之类的费用来维持，一笔固定百分比的收入将来自于已存在的国家和/或地区的广告收入。因此，那些已经存在的维持当地广播服务的广告收入基础，将会受到影响，或许是重大的影响。 （美国通信委员会，1990c）全 国 广 播 工 作 者 协 会 在 整 个 美 国 无 线 电 通 信 工 业 总 计 经 济 基 础 大 约 五 分 之一 的 基 础 上 评 估 了 一 项 国 家 收 入 直 接 的 损 失 ， 包 括 模 拟 调 幅 无 线 电 广 播 这 项 最严 重 的 损 失 。 这 项 统 计 是 基 于 当 前 国 家 和 地 区 无 线 电 通 信 的 广 告 总 收 入 而 做 出的 ， 这 些 或 许 可 能 转 换 成 以 人 造 卫 星 为 基 础 的 “超 级 站 ”服 务 在 这 些 建 立 以后 。 他 们 （ NAB） 预 测 说 “整 个 无 线 电 通 信 工 业 财 政 上 的 利 润 将 跌 至 零 如 果低 于 当 前 电 台 三 分 之 一 的 国 家 /地 区 的 广 告 转 向 卫 星 转 播 服 务 。当 然 ， 所 以 的 这 些 论 点 都 是 为 了 有 利 于 维 持 全 球 统 一 系 统 ， 争 取 建 立 一 个 有地 方 性 价 值 的 市 场 。 它 的 优 点 是 公 司 设 立 的 支 持 地 方 经 济 建 设 的 传 统 市 场 以及 政 治 因 素 . 经 济 上 保 护 他 们 自 己 的 企 业 和 市 场 的 稳 定 .在政治上,支持美国通信委员会委员会的“惯例” ，广播公司确认将根据美国通信委员会的现有制度并且和他们过去已经参股。这些条件支持着这样一种观点“美国通信委员会作为许可证的颁发者和商业上的政治保护者” 。事实上，美国通信委员会作为交换服务于当地的区域应该使该广播站（和他们赚钱的权利）得到保证。介绍11 概况新式数字广播系统 DAB（数字音频广播，现在经常叫做数字广播）是一个具有创新性的和广泛应用的广播系统，他在今后将会在全球范围内代替 AMFM音频广播服务。该系统于 1990 年由 Eureka 的 147/DAB 项目所发展起来。数字广播非常适合移动接收，并且提供了高稳定性，防止了多径接收。 它允许使用单一频率的网络，提高了频率利用率。数字广播除了具有高性能之外（单信道、双信道、多信道立体声耳机） ，还可以传输与程序有关的数据和多元的数据服务（比如交通信息、图片和动画等等） 。一个网络动态多元管理系统为自由化变成提供了可能性。在欧洲的一些国家和海外的广播组织中，网络提供商和接收设备制造商将要把运用 DAB 的数字广播服务应用在航天项目和公共服务中。DAB 与传统的广播系统有很大的差别