In order to generate multiple-access signals, each transmitter transmits information by using all or a part of channel resources. The signal of each transmitter is mapped to an OFDM time-frequency resource space as a trellis modulation path. A mobile communication system maps trellis modulation paths of a plurality of transmitters to the same resource space. In order to effectively detect and distinguish signals of a plurality of transmitters transmitted through the same channel resource space, a receiver uses a message passing method between symbols and a path connection method. The receiver uses a state space expansion method, a backward pre-decoding method, and a successive interference cancellation method to more efficiently reconstruct a discovery signal.