Simulation And Implementation Of DVB-T OFDM Modulator And Demodulator

DTTB is one of the existing digital television broadcasting systems using ground wireless transmissions. As a result of the developments in digital television transmission technology, three important digital television standards have been established, involving the ATSC standard in USA, ISDB-T standard in Japan, and DVB-T standard in Europe.Proposed as the digital television terrestrial broadcasting standard by ETSI (European Telecommunications Standards Institute), DVB-T affects the digital television field extensively. Composed of modules including Reed-Solomon (RS) codec, outer interleaver & deinterleaver, convolutional codec, inner interleaver & deinterleaver, as well as orthogonal frequency division modulation (OFDM) modem, DVB-T system employs coding OFDM (COFDM) as its key transmission technique for the feasibilities possessed by OFDM in multipath fading channel and mobile reception situation, as well as the easier implementations of frequency planning, channel estimation and frequency-domain equalization. Starting from the discussions on developments and key techniques in present digital television terrestrial broadcasting technology as well as the complete DVB-T system flow, this thesis focuses on the investigation of the OFDM modem in DVB-T system, including the constellation mapping, the pilot insertion, the fast Fourier transform (FFT) algorithm and the guard interval insertion.On the basis of the Visual Studio 2005 platform, this thesis simulates the system error performance of DVB-T system for both the 2K and 8K modes of in AWGN (Additive White Guassian Noise), Rayleigh and Rician channel. The multipath propagation channel is simulated in accordance with the models presented by the standard documentations and to compensate the multipath fading, equalization is conducted on the basis of each subcarrier. Based on the simulated system, the simulation results in the context of different coding rates, guard interval lengths and channel types are presented, which show that the system performs best when the optimum guard interval length is adopted.Besides, the thesis designs the OFDM modem on the basis of FPGA implementation, including the constellation mapping/demapping, the inverse FFT (IFFT) /FFT, the guard interval insertion/removal and so on. Several prevalent FFT algorithms are introduced, compared and evaluated in the thesis, based on which, Radix-4 and Radix-2 FFT algorithms are selected for the 2048 FFT transformation in the 2K mode. Using the pipeline structure and the CORDIC algorithm to implement the FFT module and complex multiplication respectively, the thesis implements the phase rotation by means of look-up table stored in ROM. The functional simulation results of the OFDM modem for 2K mode are presented in the thesis to validate the correctness of the design.