Abstract: The present invention relates to a multi-code multicarrier code division multiple access system in frequency-selective fading channels. According to the present invention, the transmitting device thereof uses the mapping/spectrum-spreading units to receive the plurality of substreams, map and spread the plurality of substreams, and produce a plurality of biorthogonal keying data items. The plurality of repetition units receives the plurality of biorthogonal keying data items, respectively, repeats the plurality of biorthogonal keying data items, and produces the plurality of repeated data item. The shifting units shift the plurality of repeated data items, respectively, and produce a plurality of shifted data items. The shifted data items are orthogonal to each other. Thereby, the peak-to-average-power-ratio (PAPR) is lowered.