Channel sounding method in wireless local area network system and apparatus for supporting the same

A station configured to perform channel sounding in a wireless local area network, the station comprising:

• a transceiver configured to transmit and receive signals;
• and
• a processor operatively connected to the transceiver and configured to:
• receive a 20 MHz null data packet announcement (NDPA) frame and at least one duplicate 20 MHz NDPA frame, the at least one duplicate 20 MHz NDPA frame being a duplicate of the 20 MHz NDPA frame;
• receive a null data packet (NDP) following the 20 MHz NDPA frame and the at least one duplicate 20 MHz NDPA frame, wherein a bandwidth over which the 20 MHz NDPA frame and the at least one duplicate 20 MHz NDPA frame are transmitted is same as a bandwidth over which the NDP is transmitted;
• and
• transmit a report frame for the channel sounding,
• wherein the 20 MHz NDPA frame and the at least one duplicate 20 MHz NDPA frame comprise bandwidth information indicating the bandwidth over which the 20 MHz NDPA frame and the at least one duplicate 20 MHz NDPA frame are transmitted.