The present disclosure relates to a wireless communication system and, particularly, to a method and a device therefor, the method comprising the steps of: receiving a PDCCH on the basis of a DFT-s-OFDM symbol from a base station; and obtaining DCI from the received PDCCH, wherein the PDCCH is mapped to one or more DET-s-OFDM symbols, the PDCCH is generated by means of one or more DFT calculations and one IFFT calculation applied to a plurality of modulation symbols respectively corresponding to the one or more DFT-s-OFDM symbols, and a plurality of modulation symbols input for at least one DFT calculation among the one or more DFT calculations configure one resource group.