Method for replying with acknowledgement frame, apparatus, and data transmission system

An access point (AP) in a wireless local area network (WLAN), wherein the AP comprises a processor and a communications interface, wherein

• the processor is configured to perform operations including:
• sending a scheduling frame to a plurality of stations (STAs) associated with the AP in the WLAN;
• receiving a plurality of uplink physical layer protocol data units (PPDUs) that are in response to the scheduling frame, wherein each of the plurality of uplink PPDUs comprises a first preamble and an aggregate media access control protocol data unit (A-MPDU), each A-MPDU comprises at least one A-MPDU subfield;
• calculating sending duration of a physical layer service data unit (PSDU) in a to-be-sent downlink PPDU based on a format and a sending rate that are of the downlink PPDU and based on that a length of each block acknowledgement bitmap field in a block acknowledgement frame in the downlink PPDU is a maximum quantity of bytes that is of each respective block acknowledgement bitmap field of the plurality of STAs and that is determined by the AP and the plurality of STAs in a session association phase, to generate a legacy signal (L-SIG) field of a second preamble, wherein the downlink PPDU comprises the second preamble and the PSDU, and the PSDU is the block acknowledgement frame for A-MPDUs in all the uplink PPDUs;
• generating the block acknowledgement frame, wherein the block acknowledgement frame comprises a block acknowledgement information field, the block acknowledgement information field comprises a plurality of STA information subfields, the plurality of STA information subfields have a one-to-one correspondence with the plurality of STAs, and regardless of whether all A-MPDU subfields in each of the A-MPDUs in all the uplink PPDUs are received, each STA information subfield comprises an association identifier traffic identifier (AID TID) field, a block acknowledgement starting sequence control field, and a block acknowledgement bitmap field, the AID TID field comprises an acknowledgement frame type subfield, a value of the acknowledgement frame type subfield is always 0, and a length of the block acknowledgement bitmap field in each STA information subfield is equal to a maximum quantity of bytes of a block acknowledgement bitmap field that is determined by the AP and a corresponding STA in the session association phase;
• and
• sending the downlink PPDU;
• and
• the processor is further configured to exchange information with an associated STA by using the communications interface.

A data transmission system, wherein the data transmission system comprises an access point (AP) and a plurality of stations (STAs) associated with the AP,

• wherein the AP in a wireless local area network (WLAN) comprises a processor and a communications interface, wherein the processor is configured to perform operations including:
• sending a scheduling frame to a plurality of STAs associated with the AP in the WLAN;
• receiving a plurality of uplink physical layer protocol data units (PPDUs) that are in response to the scheduling frame, wherein each of the plurality of uplink PPDUs comprises a first preamble and an aggregate media access control protocol data unit (A-MPDU), each A-MPDU comprises at least one A-MPDU subfield,
• calculating sending duration of a physical layer service data unit (PSDU) in a to-be-sent downlink PPDU based on a format and a sending rate that are of the downlink PPDU and based on that a length of each block acknowledgement bitmap field in a block acknowledgement frame in the downlink PPDU is a maximum quantity of bytes that is of each respective block acknowledgement bitmap field of the plurality of STAs and that is determined by the AP and the plurality of STAs in a session association phase, to generate a legacy signal (L-SIG) field of a second preamble, wherein the downlink PPDU comprises the second preamble and the PSDU, and the PSDU is the block acknowledgement frame for A-MPDUs in all the uplink PPDUs;
• generating the block acknowledgement frame, wherein the block acknowledgement frame comprises a block acknowledgement information field, the block acknowledgement information field comprises a plurality of STA information subfields, the plurality of STA information subfields have a one-to-one correspondence with the plurality of STAs, and regardless of whether all A-MPDU subfields in each of the A-MPDUs in all the uplink PPDUs are received, each STA information subfield comprises an association identifier traffic identifier (AID TID) field, a block acknowledgement starting sequence control field, and a block acknowledgement bitmap field, the AID TID field comprises an acknowledgement frame type subfield, a value of the acknowledgement frame type subfield is always 0, and a length of the block acknowledgement bitmap field in each STA information subfield is equal to a maximum quantity of bytes of a block acknowledgement bitmap field that is determined by the AP and a corresponding STA in the session association phase;
• and
• sending the downlink PPDU;
• and
• the processor is further configured to exchange information with an associated STA by using the communications interface.