A method for allocating a radio resource for a Long Term Evolution-unlicensed, LTE-U, data transmission of a communication device in an unlicensed frequency band is disclosed. The method includes the communication device determining a time gap duration until a start time of a subframe. The communication device selects a resource allocation transmission from a plurality of resource allocation transmissions as a function of the determined time gap duration. Related communication devices, methods by devices, and systems are disclosed.