1. A transmission device in a wireless communication system, comprising: a spreading unit configured to generate two data flows by applying a Conjugate Symmetric Discrete Fourier Transform (CS-DFT) spreading operation to a first complex-value data flow input thereto; a sub-carrier mapping unit configured to map each of the two data flows to sub-carriers; and a modulator configured to generate Offset Quadrature Amplitude Modulation (OQAM) signals by applying a quadrature amplitude modulation operation to the data flows mapped on sub-carriers.