Digital communication system

PURPOSE: A digital communication system is provided to improve performance of the system by transmitting highly reliable data in a low signal to noise ratio by adding an error correction coder having a state transition diagram compatible with mapping of a TCM coder. CONSTITUTION: A digital communication system includes an error correction coder for correcting an error of additional data, a MUX for muxing the data and ATSC signal, a randomizer for bypassing the additional data and randomizing the ATSC data, an RS coder for adding parity to the additional data and the ATSC data, an interleaver for interleaving the additional dat and the ATSC data of the RS coder, a TCM coder for bypassing the additional data of the interleaver and encoding the ATSC data, a VSB modulator for modulating the additional data and the ATSC data of the TCM coder, and an RF converter for converting RF of the VSB modulator.