A first station generates a first radio frame which includes a physical layer preamble, a null instruction information domain and a data section. The null instruction information domain is used for triggering an access point in another basic service set which receives the first radio frame to send a second radio frame which indicates a time for reserving a channel.

The first station sends the first radio frame.

According to an exemplary embodiment, the physical layer preamble in the first radio frame includes at least one of information indicating whether the null instruction information domain is carried, a length of the null instruction information domain, and a starting position of the null instruction information domain.

According to an exemplary embodiment, a power in the null instruction information domain is the same with or different from a power in a part of the first radio frame other than the null instruction information domain.

According to an exemplary embodiment, the null instruction information domain is invalid data for a destination station of the first radio frame.

According to an exemplary embodiment, the null instruction information domain is located between the physical layer preamble and the data section of the first radio frame, or between a signaling field and a short training sequence domain of the physical layer preamble of the first radio frame.

According to an exemplary embodiment, the physical layer preamble of the first radio frame indicates duration of the first radio frame;

a stopping time of the time indicated by the second radio frame for reserving the channel is the same with a stopping time of the first radio frame.