A method for transmitting a wake-up packet includes generating a first preamble including a first length indication indicating a length of a payload for a first receiving device, generating a wake-up packet (WUP) for a second receiving device, generating a second preamble including a second length indication of a summation of lengths of the first preamble, the payload, and the WUP, and transmitting the second preamble, the first preamble, the payload, and the WUP.