A signal interface unit in a radio system includes an external device interface configured to receive a downlink asynchronous radio carrier signal for a radio frequency carrier from an external device; a clock conversion unit communicatively coupled to the external device interface and configured to re-clock the downlink asynchronous radio carrier signal to a master clock of the radio system from the clock of the external device; and an antenna side interface configured to communicate at least one of the re-clocked downlink asynchronous radio carrier signal and a downlink digitized radio frequency signal based on the re-clocked downlink asynchronous radio carrier signal to an antenna unit.