A method and apparatus in a wireless communication system supporting a semi-static shared spectrum channel access is provided. The method and apparatus comprises: receiving system information carried by downlink channels; identifying a duration of idle period, a fixed frame period, a number of observation slots, and an index; determining a first phase based on a first time period between a starting instance of the idle period and an ending instance of the at least one observation slot, a second phase based on a second time period between the ending instance of the at least one observation slot and an ending instance of the idle period, and a third phase based on a third time period between the ending instance of the idle period and an ending instance of the fixed frame period; and identifying the downlink channels as an idle state in the at least one observation slot.