Retransmission method at time of sharing transmission opportunity in wireless LAN system, and device therefor

1. A method of performing retransmission during transmission opportunity (TXOP) sharing in a wireless local area network (WLAN) system, the method comprising:

transmitting an initial transmission frame including primary access category (AC) information and secondary AC information;

resetting a backoff timer value for the secondary AC information when there is no response to the secondary AC information of the initial transmission frame; and

retransmitting the secondary AC information according to the reset backoff timer value,

wherein a first retry counter for transmission of the primary AC information and a second retry counter for transmission of the secondary AC information independently operate.

2. The method according to claim 1 , wherein the backoff timer value for the secondary AC information is set to be equal to or greater than a backoff value for the primary AC information.

3. The method according to claim 1 , wherein the backoff timer value for the secondary AC information is set to a value obtained by adding any one of (a) a current backoff timer value for the secondary AC information, (b) an arbitrary integer selected in a range of 0 to the current backoff timer value for the secondary AC information or (c) an arbitrary integer selected in a range of 0 to a current contention window (CW) for the secondary AC information to a backoff timer value for the primary AC information.

4. The method according to claim 1 , wherein, when a value of the second retry counter reaches a predetermined threshold, the secondary AC information is no longer retransmitted in a secondary AC format.

5. The method according to claim 1 , wherein a value of the second retry counter increases by 1 when a value of the first retry counter increases by a predetermined integer multiple.

6. The method according to claim 1 , wherein the initial transformation frame for transmitting the primary AC information and the secondary AC information is transmitted in a state of including a PLCP protocol data unit (PPDU).

7. The method according to claim 1 , wherein the primary AC information and the secondary AC information are transmitted through a primary channel and a secondary channel in an orthogonal frequency-division multiple access (OFDMA) transmission scheme.

8. The method according to claim 7 , wherein a clear channel assessment (CCA) level of the primary channel is set to a value less than that of the secondary channel.

9. The method according to claim 7 , wherein:

the primary AC information is transmitted through (a) the primary channel or (b) the primary channel and the secondary channel, and

the primary AC information is not transmitted only through the secondary channel.

10. The method according to claim 1 , wherein the primary AC information and the secondary AC information are used for downlink multi-user (MU) multiple input multiple output (MIMO) transmission for transmitting information from a specific access point (AP) to a plurality of stations (STAs).

11. A station device operating in a wireless local area network (WLAN) system, the station device comprising:

a transceiver configured to transmit an initial transmission frame including primary access category (AC) information and secondary AC information in a specific transmission opportunity (TXOP);

a processor connected to the transceiver and configured to reset a backoff timer value for the secondary AC information when there is no response to the secondary AC information of the initial transmission frame and to enable the transceiver to retransmit the secondary AC information according to the reset backoff timer value; and

a memory for independently storing a first retry counter for transmission of the primary AC information and a second retry counter for transmission of the secondary information.

12. The station device according to claim 11 , wherein the station device operates as an access point (AP) or a station connected to a specific AP.