Proposed is a method for a first device for communicating wirelessly. The method can comprise a step of, from a second device, transmitting sidelink control information (SCI) comprising information relating to a demodulation reference signal (DMRS) pattern by means of a physical sidelink control channel (PSCCH) to the second device, mapping the DMRS on resources relating to a physical sidelink shared channel (PSSCH) on the basis of the information relating to the DMRS pattern and the length of a symbol duration of the PSSCH relating to the PSCCH, and transmitting the DMRS to the second device by means of the PSSCH.