Provided are a method by which a first device performs wireless communication, and a device for supporting same. The method can comprise the steps of: transmitting one or more reference signals (RSs) to a second device on the basis of first transmit power; receiving, from the second device, information related to a channel state measured on the basis of the one or more RSs; changing the first transmit power to second transmit power on the basis of the information related to the channel state; and transmitting the one or more RSs to the second device on the basis of the second transmit power.