The present invention relates to a wireless communication system and, more particularly, to a method comprising the steps of: generating a first complex symbol sequence corresponding to one time unit including a plurality of transmission symbols; generating a second complex symbol sequence by applying primary scrambling to the first complex symbol sequence on a modulation symbol basis; and repeatedly transmitting the second complex symbol sequence through a plurality of time units, wherein secondary scrambling is applied to the signals in each time unit on a transmission symbol basis, the transmission symbol including an OFDMA symbol or an SC-FDMA symbol; and an apparatus therefor.