Method and apparatus for channel access in wireless communication system using unlicensed spectrum

A base station for a wireless communication using an unlicensed band, the base station comprising:

• a transceiver to transmit and receive signals to and from at least one user equipment (UE);
• and
• a controller coupled with the transceiver and configured to:
• control to transmit data to the at least one UE using the unlicensed band,
• identify responses for the data from the at least one UE, each responses indicating at least one state of receiving the data of the at least one user equipment,
• identify a ratio of a negative acknowledgement (NACK) state to states indicated by the responses, and
• determine a contention period for a channel sensing operation based on the ratio of the NACK state,
• wherein as a result of a channel selection being configured and no response being identified, the controller is further configured to determine a NACK or discontinuous transmission (DTX) state corresponding the no response as the NACK state and a DTX state corresponding the no response being ignored from the identifying the ratio of the NACK state.