An example technique may include transmitting, by a base station via a component carrier in a licensed band, control information including a resource allocation that identifies time-frequency resources for periodical transmission opportunities to be used for the conditional transmission of discovery reference signals via a secondary component carrier in an unlicensed band, determining, prior to each transmission opportunity, whether the secondary component carrier in the unlicensed band is unoccupied, and transmitting, if the secondary component carrier in the unlicensed band is unoccupied, the discovery reference signals via the secondary component carrier in the unlicensed band using the identified time-frequency resources to one or more user devices.