【作者】 曹凡；

【导师】 周鹏；

【作者基本信息】 武汉理工大学 ， 通信与信息系统， 2010， 硕士

【摘要】 数字电视的发展代表了一个国家数字化程度的高低,中国预计2015年完成模拟电视向数字电视的转换,地面数字电视的发展显得尤为重要,国际上主要有3种地面数字电视传输标准,美国的ATSC传输标准、欧洲的DVB-T传输标准以及日本的ISDB-T传输标准。中国于2006年8月颁布了中国地面数字电视传输标准(DTMB),地面数字电视发送端的调制和接收端的解调的实现迎来了新的挑战,国家标准的实施以及数字电视接收机的性能优化直接影响数字电视的发展,因此数字电视接收机内部芯片的算法设计是关键,影响接收机性能的主要三个模块是：解码,均衡和同步。本文的主要工作在于研究和实现DTMB接收端系统的同步部分。本文首先简要介绍和比较了三大标准各自的优缺点,然后详细描述了DTMB系统的关键技术,包括星座映射、帧结构、TDS-OFDM系统等,重点分析了动态多径信道的特征,同步误差的产生原因以及对系统的影响。本文总结了国内外数字电视地面广播传输系统现有的定时恢复和频偏估计算法,提出存在的问题,发现在动态多径信道下算法研究的空间大,对于多径的处理也是一直以来研究的难点。本文研究一种基于PN帧同步,采用延迟锁相环(DLL)和滑动相关技术的定时恢复的方案,并且为了提高在动态多径信道下定时误差估计的准确性,采用选取多径进行合成运算的方法,重点研究了多径信道下寄生峰、包络内假径和工作不稳定的问题以及解决办法,算法优化后仿真分析表明高Doppler的Rayleigh信道条件下,定时误差可以控制在+／-20ppm范围内。在动态多径信道条件下频偏波动较大,难以进一步提高估计精度和扩大估计范围,本文综合考虑算法实现的复杂度,提出一种应用于国标数字电视DTMB系统频偏估计的算法改进。通过总结DTMB标准中相位旋转的初始相位的规律,修改相关计算的延迟长度和参与计算的数据长度,提高估计精度,达到频偏估计的多径合成效果。经仿真结果验证,该算法提高了动态多径信道下载波恢复模块工作的稳定性,延长了系统锁定时间,令具有高Doppler的多径信道的剩余频偏绕中心波动在正负10Hz以内,从而改善了DTMB系统频偏估计的性能。更多还原

【Abstract】 The development of digital television represents the degree of a country’s level of digital. The conversion of analogue TV to digital TV in China is expected to be completed by 2015. The development of terrestrial digital television is particularly important. Currently, there are three terrestrial digital TV transmission standards in the world. They are the U.S. ATSC, the European DVB-T and the Japan’s ISDB. In August 2006, China formulated a standard named as DTMB(Digital TV terrestrial multimedia broadcasting),this brings about a certain challenges to the realization of terrestrial digital television’s modulation and de-modulation. The implementation of national standard and the optimization of digital TV receiver performance directly affect the development of digital television, so the algorithm design of Digital TV receiver IP-chip is the key. There are three modules influenced the receiver performance. They are decoding, equalization and synchronization.The main work of this thesis is to study and realize the synchronization of DTMB digital TV receiver. In this thesis, first we introduce and compare those three standards briefly, and we describe the main technology of DTMB system, including constellation mapping, framing structure, TDS-OFDM system and so on. We focus on analyzing the characteristics of the dynamic multipath channel, synchronization error causes and influences, and also sum up the domestic and international existing timing recovery and frequency offset estimation algorithm of digital television terrestrial broadcasting transmission system, discuss the problems in algorithm. We find that the research space in the dynamic multipath channel is huge. And the multi-path processing is also a research challenge.In the thesis, we do some research on a timing recovery algorithm methodology based on PN-sequence frame synchronization, delay-locked Loop and sliding correlation technology. And in order to improve the accuracy of the timing error estimation in the dynamic multi-path channel, we synthesize different echoes correlation results; focus on the research of parasitic peak, pseudo echoes in the envelope and the instability. Computer simulation illustrates timing error can be controlled within the scope of+/-20ppm in the Rayleigh channel with high Doppler frequency.For the low performance of frequency offset estimation module in the dynamic multi-path channel and the difficulty of improving the estimation accuracy and broadening the scope of frequency offset estimation, we proposed an algorithm of frequency offset estimation in DTMB System. The main research work is the discovery of the rules of preliminary phase of frame head in phase shift mode, and utilizing the rules to optimize the fluctuation of frequency offset in dynamic multi-path channel. We changed the delay length and data length in correlation. Computer simulation illustrates the superior performance of the proposed algorithm in the estimation accuracy and the stability of remaining frequency offset. The remaining frequency offset fluctuates within+/-10Hz in high-Doppler multi-path channel, thus improving frequency offset estimation performance in the DTMB system.更多还原