Downlink acknowledgment in response to uplink multiple user transmission

1. A method for transmitting an ACKnowledgement (ACK) in response to uplink data received from a plurality of Stations (STAs) by an Access Point (AP) in a Wireless Local Area Network (WLAN), the method comprising:

transmitting, to the plurality of STAs, a frame triggering transmission of a plurality of uplink data units from the plurality of STAs;

receiving a Physical layer Protocol Data Unit (PPDU) frame including a plurality of uplink data units from the plurality of STAs a predetermined Inter-Frame Space (IFS) after transmitting the trigger frame; and

transmitting an ACK frame including ACKs for the plurality of data units from the plurality of STAs,

wherein the ACK frame includes one or more ACK fields respectively corresponding to one or more of the plurality of STAs,

wherein each of the one or more ACK fields includes a first subfield including identification information about a STA, a second subfield indicating block ACK or ACK, and a third subfield indicating a Traffic Identifier (TID),

wherein when the second subfield included in the ACK field indicates block ACK, the ACK field includes block ACK bitmap information and block ACK starting sequence control information, and

wherein when the second subfield included in the ACK field indicates ACK, the ACK field does not include the block ACK bitmap information and the block ACK starting sequence control information.

2. The method according to claim 1 , wherein when a data unit is received without an error from at least one of the plurality of STAs, a frame exchange procedure initiated by the trigger frame is determined to be successful.

3. The method according to claim 1 , wherein when a frame exchange procedure initiated by the trigger frame is determined to be successful, channel access of the AP is performed using a first IFS, and

when the frame exchange procedure initiated by the trigger frame is determined to be failed, channel access of the AP is performed using a second IFS, and

wherein the first IFS is shorter than the second IFS.

4. The method according to claim 1 , wherein when the PPDU frame is determined to be received without an error, channel access of the AP is performed using a Distributed coordination function Inter-Frame Space (DIFS).

5. The method according to claim 1 , wherein when all of the data units received from the plurality of STAs have errors, reception of the PPDU frame at the AP is determined to have an error.

6. The method according to claim 5 , wherein when the reception of the PPDU frame is determined to have an error, channel access of the AP is performed using an Extended Inter-Frame Space (EIFS).

7. The method according to claim 1 , wherein information transmitted from a PHYsical (PHY) layer of the AP to a Medium Access Control (MAC) layer of the AP includes information indicating end of reception, and

wherein the information indicating end of reception includes a parameter indicating whether a reception error occurs to each of the plurality of STAs or each of the plurality of subchannels.

8. The method according to claim 7 , wherein the information indicating end of reception is a PHY-RXEND.indication primitive and the parameter indicating whether a reception error occurs to each of the plurality of STAs or each of the plurality of subchannels is a USER_INDEX parameter.

9. A method for receiving an ACKnowledgement (ACK) in response to uplink data transmitted to an Access Point (AP) by a Station (STA) in a Wireless Local Area Network (WLAN), the method comprising:

receiving, from the AP, a frame triggering transmission of a plurality of uplink data units from the STA and one or more other STAs;

transmitting a Physical layer Protocol Data Unit (PPDU) frame including an uplink data unit of the STA a predetermined Inter-Frame Space (IFS) after receiving the trigger frame, when the other one or more STAs transmit one or more data units; and

receiving an ACK frame including ACKs for the plurality of data units from the plurality of STAs,

wherein the ACK frame includes one or more ACK fields corresponding to one or more of the plurality of STAs, respectively,

wherein each of the one or more ACK fields includes a first subfield including identification information about a STA, a second subfield indicating block ACK or ACK, and a third subfield indicating a Traffic Identifier (TID),

wherein when the second subfield included in the ACK field indicates block ACK, the ACK field includes block ACK bitmap information and block ACK starting sequence control information, and

wherein when the second subfield included in the ACK field indicates ACK, the ACK field does not include the block ACK bitmap information and the block ACK starting sequence control information.

10. The method according to claim 9 , wherein when all of the data units received from the plurality of STAs have errors, reception of the PPDU frame at the AP is determined to have an error.

11. The method according to claim 10 , wherein when the reception of the PPDU frame is determined to have an error, an IFS for channel access of the AP is set to an Extended Inter-Frame Space (EIFS).

12. The method according to claim 9 , wherein when the AP receives a data unit from at least one of the plurality of STAs without an error, a frame exchange procedure initiated by the trigger frame is determined to be successful.

13. The method according to claim 9 , wherein when the AP determines that a frame exchange procedure initiated by the trigger frame is successful, an IFS for channel access of the AP is set to a first IFS, and

when the AP determines that the frame exchange procedure initiated by the trigger frame is failed, the IFS for the channel access of the AP is set to a second IFS, and

wherein the first IFS is shorter than the second IFS.

14. The method according to claim 9 , wherein when the PPDU frame is determined to be received without an error, an IFS for channel access of the AP is set to a Distributed coordination function Inter-Frame Space (DIFS).

15. The method according to claim 9 , wherein an ACKTimeout for the STA is determined by the following equation,

ACKTimeout= a SIFSTime+ a SlotTime+ a PHY-RX-Start-Delay+ X

where aSIFSTime is a Short Inter-Frame Space (SIFS), aSlotTime is a slot time, aPHY-RX-Start-Delay is a delay time until a reception time at a physical layer, X is an ACKTimeout correction value.