Research And Implementation Of Channel Modulation Based On DTMB Standard

Terrestrial digital television transmission standard is the standard of digital television transmission system. According to the requirement of terrestrial digital TV transmission system, China has formulated a standard named as DTMB (Digital TV terrestrial Multimedia Broadcasting). This standard was officially announced in August 2006 and has become the only mandatory standard in the field of china's broadcasting. DTMB uses innovative 3780-point OFDM technology, which brings about a certain challenges to the realization of terrestrial digital television's modulation and demodulation.The main work of this thesis is to study and realize the modulation of DTMB transmitter system. 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 this thesis, first we introduce and compare those three standards briefly, then we describe the structure and characteristics of DTMB system's modulator, we analysize the channel characteristic and introduce the OFDM modulation technology, the FPGA realizations are given for constellation mapping module, convolutional interleaving module and Frame build module and 3780-point FFT module which compose the DTMB system's modulator. At last we describe each module with Verilog and realize them in the Quartus II environment.Since the depth (B) and the width (M) of the convolution interleaving module are quite large in DTMB (B=52, M=520; B=52, M=720), the traditional way of using shift register to realize interleaving is not suitable here any more. Acording to this situation we use an entire RAM to realize the interleaving module's function. Combined with MATLAB and SiganTap II, we prove that the interleaving result is correct. Through analysis, using of block RAM to achieve interleaving may simplify the clock and the data management and save the system resources.3780-point IFFT is one of most important and hardest part in the DTMB system. As a result of the modulation integer's non-based 2 particularities, it is not suitable to use base-2, base-4 FFT here. Acording to this situation, we use PFA and the WFTA non-base 2 FFT arithmetic to realize the 3780-point FFT. With the PFA and WFTA, the 3780-point IFFT can be changed to 6 parts: 7 WFTA, 9 WFTA, 5 WFTA, 3 WFTA, 4 WFTA and the twiddle factor calculation. The entire IFFT system processing all of the WFTA algorithms respectively and reusing the same memory together to complete the index mapping make the whole structure easy to understand and save the resources at the same time. In this thesis, we introduce the process of 3-point WFTA in details, and on this basis, we describ the process of 3780 FFT's realization, and design it in the Quartus II enviroment.