Digital transmission apparatus using differential coding and forward error correction

A digital transmission apparatus comprising:

• in the transmission side,
• block encoding means, consisting of parallel n-units, for performing block encoding based on the same logic for FEC, with respect to parallel n-channel digital signals to be transmitted, n being an integer of 2 or more;
• differential encoding means for performing differential encoding with respect to the parallel n-channel signals, which were block-encoded by the block encoding means, as inputs;
• and
• 2.sup.n multi-level modulation means for modulating a carrier by the parallel n-channel differentially-encoded signals obtained by the differential encoding means;
• and
• in the receiving side,
• detection means for demodulating and decoding the signal which was differentially encoded and 2.sup.n -multi-level-modulated, and for outputting parallel n-channel demodulated and decoded signals;
• memory means, consisting of parallel n-units, for storing the parallel n-channel demodulated and decoded signals obtained by the detection means;
• syndrome calculation means, consisting of parallel n-units, for calculating syndrome data for detecting an error bit position included in each of the parallel n-channel signals stored in the memory means;
• first selection control means for selecting and outputting each syndrome calculation result with respect to the parallel n channels in turn;
• error bit position detecting means for performing time-series detection of each error bit position based on the syndrome calculation results supplied by the first selection control means;
• second selection control means for distributing error bit position detection results, detected by the error bit position detecting means, into each corresponding channel;
• and
• error correcting means, consisting of parallel n-units, for error-correcting error bits included in the parallel n-channel signals store in the memory means based on the error bit position detection results distributed, and for outputting the corrected signals, and
• further comprising delay means for delaying the parallel n-channel signals by different delay times for each channel, so as to input the parallel n-channel syndrome calculation results into the first selection control means in turn.