The input TS is randomized and then sent to the FEC encoder block. The FEC encoder creates concatenated code of Bose and Ray-Chaudhuri (BCH) and LDPC code. The outer code is the BCH (752,762) block code, while the inner code is the LDPC code. There are three different codes with similar structure, which are LDPC (7493, 3048), LDPC (7493, 4572,) and LDPC (7493, 6912). The encoded bit stream is mapped to the constellation and interleaved by a convolutional time-domain interleaver and a frequency-domain block interleaver. The time-domain interleaver has two modes: M=240 and M=720. The frequency-domain interleaver applies only for multi-carrier. The modulation schemes supported by the standard are 4QAM-NR, 4QAM, 16QAM, 32QAM, and 64QAM.
The modulation scheme, LDPC rate, and time interleaver mode are referred to as system information (SI). SI is encoded using a 32-bit Walsh code. The multiplexing block combines 3744 data symbols and 36 information symbols into one frame with 3780 symbols. These 3780 symbols are processed by the frame body processing block. In the case of multi-carrier mode (C=3780), these 3780 symbols are converted to the orthogonal frequency division multiplexing (OFDM) signal using a 3780-point inverse discrete fourier transform (IDFT). In the case of the single-carrier mode (C=1), the 3780-point IDFT is by-passed. The 3780 symbols form one frame body.
The key parameters of China DTV standard are summarized in Table 3. It is clear from the review of the air-interface specification that the GB20600-2006 standard accommodates significantly higher Doppler rates and faster channel estimation, which directly translate into higher mobile and vehicular speeds.
While other countries around the world developed their digital TV standards a number of years ago, the GB20600-2006 standard is a much more recent development. Standard development began in 2000 at China’s DTV Technology Research Center.
While working closely with the officials on China’s standards board, the research team studied the digital television standards of various countries around the world, including Europe’s DVB-T and ATSC in United States. They adopted and improved on the best features of each. Motivated by a self-imposed deadline to deliver free-to-air HDTV to consumers for the 2008 Beijing Olympics, China’s standard focus from the beginning was primarily on the user experience.
The core technology that empowers the GB20600-2006 standard is Time Domain Synchronous – Orthogonal Frequency Division Multiplexing (TDS-OFDM), created by Legend Silicon Corp. and developed jointly with Tsinghua University in Beijing. The GB20600-2006 standard—with TDS-OFDM at its core—is inherently more robust than other DTV standards. While it is being deployed at a rapid rate for fixed applications, it can cost effectively be used to adapt broadcast technology for more interactive and specialized programs and services for mobile audiences.