A method of transmitting a frame by a device in a wireless communication network is provided. The device generates a first symbol having a first subcarrier spacing where a symbol duration of the first symbol, excluding a guard interval, has a first length. The device generates a second symbol having a second subcarrier spacing narrower than the first subcarrier spacing wherein a symbol duration of the second symbol, excluding a guard interval, has a second length that is twice the first length. The device transmits a frame including the first symbol and the second symbol.