The present disclosure relates to a wireless communication system. Specifically, provided is a method and an apparatus for supporting same, the method comprising the steps of: obtaining random access procedure-related message A, message A including a physical random access channel (PRACH) preamble and a physical uplink shared channel (PUSCH); transmitting message A; and receiving random access procedure-related message B as a response to message A, wherein the PUSCH comprises a demodulation reference signal (DM-RS), and PRACH preamble is mapped to (i) one or more DM-RS ports and (ii) one or more DM-RS sequences on the basis of indices of respective (i) one or more DM-RS ports and indices of respective (ii) one or more DM-RS sequences.