An apparatus, working as an access point, AP, in a WLAN, wherein a time domain of the WLAN includes a contention window and a scheduling window, wherein the AP obtains a right to use a channel in the contention window and enters the scheduling window, which is a time length during which a communication between the AP and a station is scheduled by the AP, wherein the apparatus comprises: a sending module, configured to within the scheduling window, send multiple downlink, DL, parts, to a station, wherein each DL part includes multiple resource blocks each associated with one of multiple stations; wherein the multiple DL parts are used to trigger the transmission of multiple uplink, UL, parts; and a receiving module, configured to within the scheduling window, receive the multiple UL parts triggered above, wherein each UL part includes another multiple resource blocks each associated with one of the multiple stations; wherein the UL parts and the DL parts are alternated; wherein a first DL part located after a first alternation includes: a first Legacy preamble and a first high efficiency WLAN, HEW, preamble, wherein the first HEW preamble comprises a HE-SIG, a HEW short training sequence, STF, and a HEW long training sequence, LTF; wherein the first ULpart located after a second alternation includes: a second Legacy preamble and a second HEW preamble, wherein the second HEW preamble comprises a HE-SIG, a HEW-STF and a HEW-LTF; wherein the first legacy preamble and the second legacy preamble are compatible with the IEEE 802.11n or IEEE 802.11ac and comprise a legacy-short training field L-STF, a legacy-long training field L-LTF, and a legacy-signaling field L-SIG and the first and the second HEW preamble are used in a next-generation of IEEE 802.11ac; and wherein each DL part includes data to multiple STAs in their respective radio resource block and in each UL part includes data of multiple STAs in their corresponding resource blocks to be sent to the AP. a sending module, configured to within the scheduling window, send multiple downlink, DL, parts, to a station, wherein each DL part includes multiple resource blocks each associated with one of multiple stations; wherein the multiple DL parts are used to trigger the transmission of multiple uplink, UL, parts; and a receiving module, configured to within the scheduling window, receive the multiple UL parts triggered above, wherein each UL part includes another multiple resource blocks each associated with one of the multiple stations; wherein the UL parts and the DL parts are alternated; wherein a first DL part located after a first alternation includes: a first Legacy preamble and a first high efficiency WLAN, HEW, preamble, wherein the first HEW preamble comprises a HE-SIG, a HEW short training sequence, STF, and a HEW long training sequence, LTF; wherein the first ULpart located after a second alternation includes: a second Legacy preamble and a second HEW preamble, wherein the second HEW preamble comprises a HE-SIG, a HEW-STF and a HEW-LTF; wherein the first legacy preamble and the second legacy preamble are compatible with the IEEE 802.11n or IEEE 802.11ac and comprise a legacy-short training field L-STF, a legacy-long training field L-LTF, and a legacy-signaling field L-SIG and the first and the second HEW preamble are used in a next-generation of IEEE 802.11ac; and wherein each DL part includes data to multiple STAs in their respective radio resource block and in each UL part includes data of multiple STAs in their corresponding resource blocks to be sent to the AP. <EOS>