Disclosed is a digital communication system. A transmission system includes an error correction encoder part carrying out an error correction encoding for additional data inputted through a first path, a multiplexer (MUX) part, a control part, a channel coding part carrying out an RS encoding and a TCM encoding, and a VSB transmission part modulating the channel-coded data by a VSB method and outputting the modulated data. A receiver system includes a tuner part receiving and tuning additional data and ATSC data transmitted through a same channel, a TCM decoder decoding and outputting the ATSC data and additional data, a deinterleaver deinterleaving data outputted from the TCM decoder, a demultiplexer demultiplexing along a first path (ATSC) or a second path (additional data) in accordance with a kind of output data of the deinterleaver, a limiter carrying out a hard decision on data outputted by the first path, an ATSC decoder part including a derandomizer, and an additional error correction decoder part decoding additional-error-encoded data on additional data outputted through the second path.