A wireless device generates a Legacy preamble, a 20 MHz Orthogonal Frequency Division Multiplexing (OFDM) symbol, and a Wake-Up (WU) signal portion. The Legacy Preamble includes a Legacy Short Training Field (L-STF), a Legacy Long Training Field (L-LTF) and a Legacy Signal (L-SIG) field. The 20 MHz OFDM symbol has a duration of 4 μs. The WU signal portion has a frequency bandwidth that is narrower than a frequency bandwidth of the Legacy preamble. The wireless device transmits a frame, which includes transmitting the Legacy preamble, transmitting the 20 MHz OFDM symbol immediately after transmitting the Legacy preamble, and transmitting the WU signal portion immediately after transmitting the 20 MHz OFDM symbol.