A station may receive a frame transmitted to a plurality of STAs. The frame may indicate a first frequency resource allocated for the STA and a second frequency resource allocated for another STA of the plurality of STAs. The STA may transmit a data frame using the first frequency resource and receive an acknowledgement frame that acknowledges receipt of the data frame. The STA may receive a MU RTS frame transmitted to the plurality of STAs and may subsequently transmit a CTS frame in response to receipt of the MU RTS frame. The RTS/CTS transmissions may occur prior to transmission of the data frame.