The first wireless transmission chip is configured to send 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.

According to an exemplary embodiment, the physical layer preamble in the first radio frame indicates the time for reserving the channel;

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 time indicated by the first radio frame for reserving the channel.