Previously known as DMB-T/H, the DTMB is a merger of the standards ADTB-T, DMB-T and TiMi ; this last one is the standard proposed by the Academy of Broadcasting Science in 2002. At first, neither Shanghai Jiao Tong University nor Tsinghua had enough political strength to make their own technology become the unique standard, so the final decision was to opt for a double standard, merged with the TIMI 3 standard, responding to a need for backward compatibility. The DTMB was created in 2004 and finally became an official DTT standard in 2006.
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 and mobile digital terrestrial television.
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 for error correction, 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 an 8 MHz channel bandwidth. Finally the signal is modulated to put it in the corresponding frequency band.
Features
Bit-rate: from 4.813 Mbit/s to 32.486 Mbit/s
Combination of SD, HD, and multimedia services
Flexibility of services
Time and frequency domain of data-processing
Broadcasting of between 6 and 15 SD channels and 1 or 2 HD channels
