A method comprises constructing, by an access point (AP), a radio frame within a scheduling window, the radio frame including at least a preamble part compatible with an existing IEEE 802.11 preamble legacy preamble, a preamble part used in a next-generation IEEE 802.11 standard (HEW preamble), and the first downlink subframe (DL subframe); sending the Legacy preamble, the HEW preamble and the first DL subframe in the radio frame; receiving at least one uplink subframe (UL subframe) located after the first DL subframe; wherein each of the at least one UL subframes is triggered by one DL subframe located before the UL subframe.