NACK frame for HARQ operation

1. A method in a wireless local area network (WLAN) system, the method comprising:

transmitting, by a transmitting station (STA), a physical protocol data unit (PPDU) to a receiving STA,

wherein the PPDU includes a legacy signal (L-SIG) field including a length field related to a length of the PPDU, wherein the length field is set to a value satisfying a condition that a remainder is zero when the length field is divided by three,

wherein the PPDU further includes a repeated legacy signal field (RL-SIG) field which is a repeat of the L-SIG field and is contiguous to the L-SIG field,

wherein the PPDU further includes a first control signal field which is contiguous to the RL-SIG field, wherein the first control signal field includes three-bit information indicating a physical version of the PPDU, one-bit information indicating whether the PPDU is related to an uplink (UL) or downlink (DL), information related to an identifier of a basic service set (BSS) related to the PPDU, and information related to a duration of transmission opportunity (TXOP),

wherein the PPDU further includes a second control signal field including control information related to a hybrid automatic repeat request (HARQ) operation, wherein the second control information includes a transmitter identifier (TXID), a receiver identifier (RXID), and a new data indicator (NDI) related to the HARQ operation,

wherein the PPDU further includes a data field including a first redundancy version of transmission data;

receiving, by the transmitting STA from the receiving STA, a response which is an acknowledgment (ACK) frame or a negative ACK (NACK) frame, wherein the response includes a medium access control (MAC) header and a frame body field which is contiguous to the MAC header, wherein the MAC header includes a frame control field, wherein the frame control field includes a type field having a length of 2 bits and a subtype field having a length of 4 bits, wherein a combination of the type field and the subtype field indicates whether the response is the ACK frame or the NACK frame; and

determining, by the transmitting STA, a second redundancy version of the transmission data to be retransmitted based on whether the ACK frame or the NACK frame is received within a threshold time.

2. The method of claim 1 , wherein the second redundancy version is determined the same as the first redundancy version based on that the transmitting STA does not receive the ACK frame or the NACK frame within the threshold time,

wherein the second redundancy version is determined to be different from the first redundancy version based on that the transmitting STA receives the NACK frame within the threshold time.

3. The method of claim 1 , wherein the transmission data includes only one media access control protocol data unit (MPDU),

wherein the NACK frame is a block ACK (BA) frame,

wherein the NACK frame includes a transmitter address (TA) field,

wherein the TA field includes (i) a bit related to a failure of the receiving STA to receive the transmission data and (ii) information related to a MAC address of the receiving STA.

4. The method of claim 1 , wherein the second redundancy version is transmitted at a lower rate than the first redundancy version.

5. A transmitting station (STA) in a wireless local area network (WLAN) system, the transmitting STA comprising:

a transceiver configured to transmit or receive a radio signal; and

a processor being operatively coupled to the transceiver,

wherein the processor is configured to:

transmit a physical protocol data unit (PPDU) to a receiving STA,

wherein the PPDU includes a legacy signal (L-SIG) field including a length field related to a length of the PPDU, wherein the length field is set to a value satisfying a condition that a remainder is zero when the length field is divided by three,

wherein the PPDU further includes a repeated legacy signal field (RL-SIG) field which is a repeat of the L-SIG field and is contiguous to the L-SIG field,

wherein the PPDU further includes a first control signal field which is contiguous to the RL-SIG field, wherein the first control signal field includes three-bit information indicating a physical version of the PPDU, one-bit information indicating whether the PPDU is related to an uplink (UL) or downlink (DL), information related to an identifier of a basic service set (BSS) related to the PPDU, and information related to a duration of transmission opportunity (TXOP),

wherein the PPDU further includes a second control signal field including control information related to a hybrid automatic repeat request (HARQ) operation, wherein the second control information includes a transmitter identifier (TXID), a receiver identifier (RXID), and a new data indicator (NDI) related to the HARQ operation,

wherein the PPDU further includes a data field including a first redundancy version of transmission data;

receive, from the receiving STA, a response which is an acknowledgment (ACK) frame or a negative ACK (NACK) frame, wherein the response includes a medium access control (MAC) header and a frame body field which is contiguous to the MAC header, wherein the MAC header includes a frame control field, wherein the frame control field includes a type field having a length of 2 bits and a subtype field having a length of 4 bits, wherein a combination of the type field and the subtype field indicates whether the response is the ACK frame or the NACK frame; and

determine a second redundancy version of the transmission data to be retransmitted based on whether the ACK frame or the NACK frame is received within a threshold time.

6. The transmitting STA of claim 5 , wherein the second redundancy version is determined the same as the first redundancy version based on that the transmitting STA does not receive the ACK frame or the NACK frame within the threshold time,

wherein the second redundancy version is determined to be different from the first redundancy version based on that the transmitting STA receives the NACK frame within the threshold time.

7. The transmitting STA of claim 5 , wherein the transmission data includes only one media access control protocol data unit (MPDU),

wherein the NACK frame is a block ACK (BA) frame,

wherein the NACK frame includes a transmitter address (TA) field,

wherein the TA field includes (i) a bit related to a failure of the receiving STA to receive the transmission data and (ii) information related to a MAC address of the receiving STA.

8. The transmitting STA of claim 5 , wherein the second redundancy version is transmitted at a lower rate than the first redundancy version.