Techniques for mobile communication in an unlicensed frequency band are discussed. A network device (e.g., an evolved NodeB, or other cell network device) can generate a listen before talk (LBT) protocol in order to determine whether an unlicensed carrier of a secondary cell device is idle or busy. The LBT protocol can be generated as a one shot LBT within a two symbol duration of a potential downlink (DL) transmission burst, or multiple times within the two symbol duration. In response to an idle state detection, a discovery reference signal (DRS) can be transmitted. In response to the LBT protocol and the DRS transmission being misaligned, a reservation signal can be generated to reserve the unlicensed carrier for the DL transmission.