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.

In other exemplary schemes, each station/access point may determine one or more of the above information by default, by pre-configuration or by convention, and it is thus not needed to include corresponding information in the physical layer preamble. For example, the first station, the second station and the access points can consider that there is a null instruction information domain in all radio frames by default, and in this way it is not needed to indicate whether the null instruction information domain is carried.

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.

That is to say, after the second station receives the first radio frame, the second station can discard or ignore the null instruction information domain.

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.