28-12-2012, 12:30 PM
DIGITAL TERRESTRIAL MULTIMEDIA BROADCAST
DIGITAL TERRESTRIAL.doc (Size: 46 KB / Downloads: 30)
Introduction
DTMB is the TV standard for mobile and fixed terminals used in the People's Republic of China, Hong Kong and Macau. Although at first this standard was DMB-T/H, the official name is DTMB.
Overview
The DTMB is a merger of the following standards: ADTB-T (developed by the Shanghai Jiao Tong University, Shanghai), DMB-T (developed by Tsinghua University, Beijing) and TiMi (Terrestrial Interactive Multiservice Infrastructure), which is the standard proposed by the Academy of Broadcasting Science in 2002.At first, neither Shanghai Jiao Tong University nor Tsinghua had not enough political strength to make their own technology being the unique standard, so the final decision was to opt for a double standard, merged with the TIMI 3 standard, responding to a need of backward compatibility. The DTMB was created in 2004 and finally became an official DTT standard in 2006.
DTMB in China
• 2005 trial
• 18/08/2006 formal adoption as a DTT standard
• 2008 analogue to digital switchover
• 2015-2018 analog switch off
DTMB in Hong Kong
• 18/08/2006 formal adoption as a DTT standard
• 31/12/2007 analogue to digital switchover
• 2015 analogue switch off
DTMB in Macau
• 18/08/2006 formal adoption as a DTT standard
Countries and territories using DTMB
ASIA
• China
• Hong Kong
• Laos
• Macau
• Malaysia (Experimental)
MIDDLE EAST
• Iraq (Experimental)
• Jordan (Experimental)
• Syria (Experimental)
• Lebanon (Experimental)
Description
Besides the basic functions of traditional television service, the DTMB allows additional services using the new television broadcasting system. DTMB system is compatible with fixed reception (indoor and outdoor) and mobile digital terrestrial television.
• Mobile reception: is compatible with digital broadcasting TV in standard definition, digital audio broadcasting, multimedia broadcasting and data broadcasting service.
• Fixed reception: in addition to the previous services, also supports high definition digital broadcasting.
Modulation
The DTMB standard uses many advanced technologies to improve their performance, for example, a pseudo-random noise code as a guard interval that allows faster synchronization system and a more accurate channel estimation, Low-Density Parity-Check encoding to protect against mistakes, modulation Time Domain Synchronization - Orthogonal Frequency Division Multiplexing which allows the combination of broadcasting in SD, HD and multimedia services, etc. This system gives flexibility to the services offered to support the combination of single-frequency networks and multi-frequency networks. The different modes and parameters can be chosen depending on the type of service and network's environment. The sequence of pseudo-random pattern is defined in time domain and the information of the Discrete Fourier transform is defined in the frequency domain. The two frames are multiplexed in the time domain, resulting in Time domain synchronization.
Functional Scheme
This transmission system makes the conversion of the input signal to the output data of terrestrial TV signal. The data passes through the encoder; the error protection process FEC, through the constellation mapping process and then the interleaving processes the information to create the data blocks. The data block and the TPS information are multiplexed, and pass through the data processor to form the body structure. It combines information from the body and the head to form the frame and this is passed through the SRRC filter to become a signal within a 8 MHz channel bandwidth. Finally the signal is modulated to put it in the corresponding frequency band.