Performance Evaluation of OFDM Based Digital Video Broadcasting Systems

Abstract

Digital video broadcasting (DVB) is a widely used standard for terrestrial television transmission. Digital terrestrial television broadcasting aimed at transmitting two types of information that is global and local content. The global content aims at broadcasting over the entire network and the local content is location-specific. Broadcasting the local content using multiple transmitters at different frequencies requires additional spectrum. Therefore if this information can be transmitted in a Single Frequency Network (SFN), the system will become highly spectrally efficient and cost-effective. This can be achieved using hierarchical modulation technique. In this method, the global and local content are embedded in a single constellation before transmission. SFN also supports multicarrier modulation like Orthogonal Frequency Division Multiplexing (OFDM). At present in digital video broadcasting, OFDM is implemented with fast Fourier transform. To combat intersymbol interference in any Fourier based OFDM system, cyclic prefix is used. This cyclic prefix consumes nearly 20%-25% of the total bandwidth. As the first work of this thesis wavelet based OFDM is proposed for DVB system. In the proposed technique, inverse Fast Fourier transform (IFFT) and Fast Fourier Transform (FFT) are replaced with Inverse Discrete Wavelet Transform (IDWT) and Discrete Wavelet Transform (DWT) in the OFDM block. This proposed system was simulated without cyclic prefix. Even without cyclic prefix insertion, the system showed an improved performance compared to conventional Fourier based OFDM. newlineAt the receiver, while detecting the base layer bits and secondary layer bits, different detection rules are necessary for hierarchical modulation based systems. The detection of base layer bits requires only four rules since it is QPSK modulated and it represents the quadrant of the constellation. The detection of secondary layer bits requires the number of detection rules equal to four times the number of message points in a quadrant. This increa