BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to wireless communication and, more particularly, to a method and device for transmitting a data unit in a wireless local area network.

Related Art

Institute of Electrical and Electronics Engineers (IEEE) 802.11 based wireless local area networks (WLANs), the most popular and successful indoor wireless solutions, have evolved as a key enabling technology to cover medium to large scale enterprises, public area hot-spots, apartment complexes, and are ubiquitous in the modern world.

High Efficiency (HE) WLAN (e.g., IEEE 802.11ax) improves a spectrum efficiency and an area throughput in a dense environment. Especially, in an indoor or an outdoor environment, a purpose of the HE WLAN is to improve a performance when a lot of access points (APs) and stations (STAs) are competing.

Since a lot of APs and STAs are competing, an improved protection mechanism to prevent a collision due to simultaneous transmissions of STAs is required.

SUMMARY OF THE INVENTION

The present invention provides a method and device for transmitting a physical layer protocol data unit (PPDU) in a transmission opportunity (TXOP).

In an aspect, the method includes transmitting, by a transmitting station, a request to send (RTS) frame to a plurality of receiving stations, the RTS frame including a bandwidth field and a plurality of allocation fields, the bandwidth field indicating a first bandwidth in which the RTS frame is transmitted, each allocation field indicating a bandwidth in which a clear to send (CTS) frame is to be sent by a corresponding receiving station, receiving, by the transmitting station, a plurality of clear to send (CTS) frames as a response to the RTS frame from the plurality of receiving stations, determining, by the transmitting station, a transmission bandwidth of a PPDU to be sent by comparing the first bandwidth with a second bandwidth which is a total bandwidth indicated by the plurality of allocation fields, and transmitting, by the transmitting station, the PPDU in the determined transmission bandwidth.

When a value of the first bandwidth is equal to a value of the second bandwidth, a value of the transmission bandwidth of the PPDU may be set to a value that is equal to or smaller than the value of the first bandwidth.

When the value of the first bandwidth is not equal to the value of the second bandwidth, the value of the transmission bandwidth of the PPDU may be set to a value that is equal to or smaller than a value of a third bandwidth in which a preceding PPDU is transmitted by the transmitting station.

In another aspect, the device includes a transceiver configured to receive and transmit radio signals, and a processor coupled with the transceiver. The processor is configured to control the transceiver to transmit a request to send (RTS) frame to a plurality of receiving stations, the RTS frame including a bandwidth field and a plurality of allocation fields, the bandwidth field indicating a first bandwidth in which the RTS frame is transmitted, each allocation field indicating a bandwidth in which a clear to send (CTS) frame is to be sent by a corresponding receiving station, control the transceiver to receive a plurality of clear to send (CTS) frames as a response to the RTS frame from the plurality of receiving stations, determine a transmission bandwidth of a PPDU to be sent by comparing the first bandwidth with a second bandwidth which is a total bandwidth indicated by the plurality of allocation fields, and control the transceiver to transmit the PPDU in the determined transmission bandwidth.

