A method of operating a user equipment includes setting a user equipment to enter a public safety mode, converting the user equipment to an idle state when the user equipment enters the public safety mode, and temporarily converting the user equipment from the idle state to a partial wakeup state during the public safety mode. A public safety carrier searching is performed for device-to-device (D2D) communication between the user equipment and a neighboring equipment during the partial wakeup state. The method may efficiently support the D2D communication and reduce power consumption by changing the state of the user equipment into the idle state when entering the public safety mode and temporarily changing the user equipment into the partial wakeup state for public safety carrier searching.