【作者】 董佩；

【导师】 陈伟；

【作者基本信息】 武汉理工大学 ， 通信与信息系统， 2008， 硕士

【摘要】 高清晰度数字电视(HDTV)是当今广播行业最引人注目的焦点之一,具有很大的市场潜力,对国家的政治、经济、文化和生活等各方面都会产生深远影响。在中国地面数字电视传输标准颁布以前,世界上已经形成了三大地面数字电视标准,分别是:美国的ATSC标准(Advanced Television Systems Commitee)、欧洲的DVB-T标准(Digital Video Broadcasting-Terrestrial)以及日本的ISDB-T标准(Integrated Services Digital Broadcasting-Terrestrial)。2006年8月30日,中国标准化管理委员会发布了《数字电视地面广播传输系统帧结构、信道编码和调制》标准,并已于2007年8月1日起正式实施。该标准的颁布和实施为我国地面数字电视业务的开展奠定了基础,并全面启动了我国数字电视市场。在数字电视接收机的设计中,同步问题是首先要考虑的,同步可以说是接收机实现的基础,只有具备了可靠的同步能力,才能使系统中的其他部分,如均衡和解码,正常工作。载波恢复是同步的重要组成部分,也是本文紧紧围绕研究的课题。由于接收端本振时钟的不精确以及信道的快速衰落使得被传送信号偏离中心频谱,会导致下变频后的基带信号存在一定的频率偏移:同时,信号的相位在传输过程中也会因有线信道的时变特性、下变频电路等引起一定的抖动。这些原因所引起的频率和相位偏差都需要通过载波恢复来补偿。在本文中,笔者首先对中国地面数字电视广播传输系统进行了介绍,并针对《数字电视地面广播传输系统帧结构、信道编码和调制》标准,采用理论分析和实验结果相结合的方法提出了一种可应用于国标DTV单载波模式的双导频载波恢复算法,重点对算法的原理和结构进行了说明。该算法充分利用了国标单载波模式下双导频的特点,通过两个独立的锁频锁相环分别利用正负导频完成频偏估计,并采用环路加权求和的方式对抗多径干扰所导致的导频衰落。最后在C仿真平台上,对算法在高斯白噪声信道和多径信道等条件下的性能进行了仿真。仿真结果证明,本算法在多径信道条件下,能改善单一导频发生衰落时所导致的性能恶化,相对单导频载波恢复算法具有更好的性能。更多还原

【Abstract】 HDTV is recently one of the hot points in the broadcasting industry. It has gigantic market potential, and will influence the polity, economy, culture and life in a nation. Before Chinese DTTB standard came out, there has been three main standards of terrestrial broadcasting of digital television : ATSC（U.S.A）, DVB-T（Europe） and ISDB-T（Japan）. On August 30^th in 2006, Chinese DTTB standard GB20600-2006 was issued by the Standardization Administration of China（SAC）, and was carried into execution on August 1^st in 2007. The issue and actualization of Chinese DTTB standard established the foundation for the development of Chinese terrestrial DTV, and started up Chinese DTV market.During the process of DTV receiver designing, synchronization is principal. It is the basic of other part’s well-working, such as equalization and decoding. Carrier recovery is the chief component of synchronization, and also is the central part of this paper. Because of the imprecision of the local oscillator clock and the channel’s fast decline, transmitted signal may depart from the central frequency, which will result in the frequecy offset of the baseband signal after down-converting. At the same time, during the process of transmission, the cable channel’s time-variation and the down-converting circuit may arouse phase jitter. Both frequency offset and phase jitter need carrier recovery to compensate.In this paper, the author introduced the Chinese DTTB transmission system firstly. In succession, through theoretic analysis and simulation, this paper presented a new dual-pilot carrier recovery algorithm, which can be applied to the single-carrier mode in the national DTTB Standard and focused on illuminating the principle and structure of the new algorithm. This algorithm takes full advantage of dual-pilot under single-carrier mode, and utilizes a couple of independent FPLL to estimate frequency offset. Furthermore, this algorithm adopts weighted adding to resist pilot decline caused by multipath-interference. At the end of the paper, the algorithm was simulated under different channel condition such as AWGN, SSE and DSE, and was proved to have better performance than single-pilot carrier recovery algorithm in multipath channel.更多还原