Method and apparatus of transmitting PPDU in wireless communication system

A wireless device for transmitting a physical layer protocol data unit (PPDU) in a wireless communication system, the wireless device comprising:

• a processor configured to:
• for a first data stream associated with a first PPDU to be transmitted via a first channel, include a first data block, a first header and a first physical layer service data unit (PSDU) in the first data stream, wherein the first header indicates a modulation and coding scheme (MCS) of the first PSDU,
• for a second data stream associated with a second PPDU to be transmitted via a second channel, include a second data block, a second header and a second PSDU in the second data stream, wherein the second header indicates an MCS of the second PSDU, and
• perform a padding procedure to at least one of the first data stream and the second data stream so that a time duration during which the first data stream is transmitted and a time duration during which the second data stream is transmitted have an equal time duration;
• and
• a transmitter configured to transmit the first data stream and the second data stream by using the first PPDU and the second PPDU.