Method, device, and system for signal transmission in unlicensed band

A base station performing a downlink transmission in a specific cell in a cellular wireless communication system, the base station comprising:

• a wireless communication module;
• and
• a processor,
• when the downlink transmission includes a physical downlink shared channel (PDSCH) and a channel in which the downlink transmission is performed is sensed to be idle for a first predefined interval, wherein the processor is configured to perform backoff procedure after the first predefined time to perform the downlink transmission, and
• when the downlink transmission includes a Discovery Reference Signal (DRS) and does not include the PDSCH, and the channel in which the downlink transmission is performed is sensed to be idle for a second predefined interval, wherein the processor is configured to perform the downlink transmission immediately after the second predefined interval.