A method of transmitting a data frame by a station in a wireless local area network (WLAN), A station obtains a transmission opportunity (TXOP) for a bandwidth. The TXOP indicates an interval of time during which the station has a right to initiate frame exchange sequences onto a wireless medium. The station selects a transmit bandwidth parameter of a non-initial data unit of a plurality of data units from available bandwidth parameters. The available bandwidth parameters include a first available bandwidth parameter which is same as a transmit bandwidth parameter of a preceding data unit of the plurality of data units and a second available bandwidth parameter which is narrower than a transmit bandwidth parameter of the preceding data unit. The station transmits, during the TXOP, the non-initial data unit according to the transmit bandwidth parameter of the non-initial data unit.