【作者】 高超；

【导师】 侯春萍；

【作者基本信息】 天津大学 ， 通信与信息系统， 2009， 硕士

【摘要】 随着社会和信息技术的不断发展,人们希望在任何地方,任何时间都能获得多媒体的信息服务,手机电视/移动多媒体设备应运而生。陆地移动多媒体广播(Terrestrial Mobile Multimedia Broadcasting简称T-MMB)标准是我国手机电视/移动多媒体的国家标准,具有一定的自主知识产权。因此,对基于该标准的接收系统进行研究,具有十分重大的意义。解调是数字接收机必须完成的关键功能。本文通过研究T-MMB系统的帧结构和差分OFDM系统,在复杂的多径信道下提出并仿真实现了一整套适用于T-MMB的解调算法,希望籍此为T-MMB数字接收机的设计提供一定的借鉴。本论文深入研究了T-MMB中的解调算法,详细分析了各种非理想同步对T-MMB系统的影响。分析表明,T-MMB系统对于各种误差非常敏感,符号误差和采样时钟偏差将会引入码间干扰,载波偏差导致子载波间干扰的发生,帧同步误差会导致发送端和接收端的信息起始位置的不一致。最后本文提出了一套适合于T-MMB系统的同步方案,包括:帧同步、载波同步、符号同步和采样时钟同步。帧同步算法是利用能量比的方法,检测T-MMB帧中的空符号。载波频率同步算法包括小数倍频偏粗估计、整数倍频偏估计和小数倍频偏细估计。符号同步也包括符号粗同步和符号细同步。其中小数倍频偏粗估计和符号粗同步算法是利用循环前缀的最大似然估计。整数倍频偏估计、符号细同步和采样时钟同步是在频域下利用相位参考符号进行的数据辅助估计。小数倍频偏细估计是在时域下利用相位参考符号进行的估计。通过对各部分算法性能的仿真,我们可以得到如下结论:帧同步算法稳定,有很好的抗多径性能;载波频偏估计算法性能优越,估计误差的方差与克拉美罗界比较接近;符号和采样时钟同步算法都是基于相位参考符号,二者可以并行、独立地估计相应的同步参数,缩短了捕获周期,实现了通信的高效传输。各部分算法估计准确,便于数字化实现,本文设计的解调算法具有很强的抗多径衰落的特性。更多还原

【Abstract】 As the development of society and information technology, people want to access to the multimedia service wherever and whenever, so the mobile multimedia equipment comes out. Terrestrial Mobile Multimedia Broadcast standard is the national mobile phone TV/mobile multimedia standard. Because of the independent intellectual property rights in some degree, it is important for us to develop receive system based on this standard.Demodulation is the key function of digital receiver. This paper implements the T-MMB demodulation and synchronization algorithm in multi-path channels by studying the frame structure of T-MMB and differential OFDM system.This paper studies demodulation algorithm deeply. The paper discusses some non-ideal synchronization effects on the performance of T-MMB digital system in detail. The study shows that the T-MMB system is very sensitive to synchronization errors, symbol offset and sampling offset would introduce inter-symbol interference, and frequency offset of carrier would result in inter-carrier interference, and errors in frame synchronization would lead to the difference in starting signals between the transmitter and receiver.This paper also proposes a synchronization method that fits T-MMB system well, it includes: frame synchronization, carrier synchronization, symbol and sample synchronization. Frame synchronization algorithm is in use of the null symbol, using the power ratio method ; fine carrier offset and coarse symbol offset are estimated by using maximum likelihood estimation based on cyclic prefix; the phase reference symbol is used in integer carrier offset, fine symbol offset and sample offset estimation.The result of simulation indicates that the frame synchronization algorithm is robust to multi-path; carrier frequency estimation algorithm has advanced performance, the error variance is close to MCRB; the symbol and sample synchronization algorithm are based on phase reference symbol, they can work independently, in this way, the capture period is shortened and high efficiency of communication is implemented. The estimation algorithm is convenient to realize in digital. The demodulation algorithm in the paper is stable to multi-path.更多还原