Analysis and Performance Comparison of DVB-T and DTMB Systems for Terrestrial Digital TV

Ming Liu, Matthieu Crussière member IEEE, Jean-François Hélard senior IEEE, Oudomsack Pierre Pasquero Institute of Electronics and Telecommunications of Rennes (IETR) Rennes, France {first name. last name}@insa-rennes.fr

Abstract— Orthogonal frequency-division multiplexing (OFDM) is the most popular transmission technology in digital terrestrial broadcasting (DTTB), adopted by many DTTB standards. In this paper, the bit error rate (BER) performance of two DTTB systems, namely cyclic prefix OFDM (CP-OFDM) based DVB-T and time domain synchronous OFDM (TDS-OFDM) based DTMB, is evaluated in different channel conditions. Spectrum utilization and power efficiency are also discussed to demonstrate the transmission overhead of both systems. Simulation results show that the performances of the two systems are much close. Given the same ratio of guard interval (GI), the DVB-T outperforms DTMB in terms of signal to noise ratio (SNR) in Gaussian and Ricean channels, while DTMB behaves better performance in Rayleigh channel in higher code rates and higher orders of constellation thanks to its efficient channel coding and interleaving scheme. Keywords-Digital TV; DVB-T; CP-OFDM; DTMB; TDS- OFDM I. INTRODUCTION Transition from analog to digital television (DTV) is a trend worldwide. DTV services can be delivered via satellite, cable and terrestrial broadcasting. Due to its flexibility to both stationary and mobile applications, digital terrestrial television broadcasting (DTTB) has attracted more and more interest in recent years. Nowadays, there are three main DTTB standards around the world: Digital Video Broadcasting-Terrestrial (DVB-T) [1] in Europe, the trellis-coded 8-level vestigial side band (8-VSB) modulation system developed by Advanced Television System Committee (ATSC) [2] in North America, the Integrated Services Digital Broadcasting-Terrestrial (ISDB- T) [3] in Japan. Among them, DVB-T plays the most important role. Since first approved in 1997, DVB-T has become the dominant terrestrial broadcasting standard in Europe and is also popular in other continents. By June 2008, DVB-T services have been launched by 33 countries and territories. After 12 years of developing, the Chinese Digital Terrestrial/Television Multimedia Broadcasting (DTMB) standard [4] was finally ratified in August 2006, and began to be a mandatory national standard in August 2007. DTMB consists of single carrier modulation (C = 1) and multicarrier modulation (C = 3780) which are originated from two former proposals: the single-carrier ADBT-T (Advanced Digital Television Broadcasting-Terrestrial) and the multi-carrier DMB-T (Digital Multimedia/TV Broadcasting-Terrestrial) respectively, providing flexible combinations of working modes for different application scenarios. Because of the enormous TV market in China and the novel signal processing techniques integrated in it, the Chinese DTMB draws great interests from both industries and researchers. The orthogonal frequency-division multiplexing (OFDM) is definitely the most popular technique adopted by majority of DTTB standards (DVB-T, ISDB-T and DTMB). This is due to its robustness to frequency selective fading. By implementing inverse fast Fourier transform (IFFT) and FFT at transmitter and receiver sides respectively, OFDM transforms a high speed serial data flow to a set of low speed parallel ones at orthogonal flat fading sub-channels. Traditionally, a cyclic prefix (CP) is inserted between two consecutive OFDM symbols as guard interval (GI). This solution has been chosen for many standards, namely for
DVB-T and ISDB-T. The length of the GI is designed to be longer than that of channel memory. By discarding the CP at the receiver, the inter symbol interference (ISI) is then removed from the received signal. With the assistance of CP, the linear convolution between transmitted signal and channel impulse response (CIR) converts into a circular one i.e. the channel convolution effect is turned to be a set of parallel attenuations in the discrete frequency domain. Hence, the equalization in OFDM can be performed by simply multiplying a coefficient on each subcarrier at the receiver. Thus, the equalization complexity of OFDM is significantly low compared with a time domain equalizer. As the samples for the CP do not convey useful data, several researchers proposed to replace the CP by known pseudo noise (PN) sequences. This becomes the time domain synchronous OFDM (TDS-OFDM [5], also known as pseudo random postfix OFDM, PRP-OFDM [6] and known symbol padding OFDM, KSP-OFDM [7]). Besides serving as GI, the PN sequence can also be exploited to make channel estimation and synchronization in the time domain. Hence, it is not necessary to insert scattered and continual pilots to the OFDM symbols, which increases t

…(Full text truncated)…