1. A method of transmitting an uplink (UL) physical protocol data unit (PPDU) in a wireless LAN (WLAN) system, the method performed by a station (STA) comprising:receiving, from access point (AP), a trigger frame including resource allocation information related to transmission of the UL PPDU; and
transmitting, to the AP, the UL PPDU based on the trigger frame,
wherein the UL PPDU comprises (i) a first part including at least one of a legacy (L)-short training field (STF), a L-long training field (LTF), an L-signal (SIG) field, and a high efficiency (HE) SIG-A field and (ii) a second part including at least one of a HE-STF, a HE-LTF, and a data field;
wherein the second part is transmitted on a specific frequency resource represented by the resource allocation information,
wherein the first part is transmitted on the one or more 20 MHz channel in a frequency domain including the specific frequency resource,
wherein the one or more 20 MHz channel is determined based on a size of a bandwidth of the specific frequency resource.