The Research On Channel Estimation And Equalization In DTMB Systems

After years of discussion and test, China issued the merged standard for terrestrial digital TV broadcasting, which is named Digital Television/Terrestrial Multimedia Broadcasting (DTMB). The contents of this merged standard include many popular techniques like OFDM and LDPC. This paper is about methods of channel estimation and designs of equalizer for DTMB.In the first chapter, the history of digital television broadcasting is introduced. The development of digital terrestrial broadcasting in China is also presented.In the second chapter, theory of equalization is reviewed. Firstly, the multipath fading and Doppler spread in wireless communication is briefly analyzed. Then equalization in time domain is introduced. After that, the multi-carrier techniques and frequency domain equalizations for OFDM system are presented.Based on the knowledge of OFDM system, equalization for OFDM is studied in the third chapter. At the beginning, two methods for channel estimation are introduced. Both of them are based on the training sequences defined in DTMB. The method based on cyclic convolution can produce high quality estimation results. While the method with variable-length FFT window may be used in almost all circumstances. Then, the equalization process for TDS-OFDM system is analyzed. The process includes PN cancellation, reconstruction of cyclic convolution and computation of likelihood information.In the fourth chapter, equalizer designs for single-carrier transsimission are studied. Firstly a frequency domain equalization process called SC-FDE is analyzed. The MMSE criterion is used to derive an equalization expression. Then the bit error equation is used to analyze the Decision Feed Back equalizer. As DTMB uses the NR code to improve DFE's performance in low SNRs, a MAP decoder for the code is presented and the results of feedback equalization is given. After that a DFE structure with frequency domain pre-equalization is introduced. The design of pre-equalizer is briefly studied.Chapter Five gives some simulation results using Brazil channel models and Rayleigh channel model. The simulation compares the two estimation methods. The equalizers used in single-carrier mode are also discussed. At the end the thresholds of system in each static channel model are gotten by simulation with equalizer and LDPC decoder.In the end, a summary of this paper and future directions are given.