A method for operating a first communications controller adapted for operation in a first communications band in a communications system with a plurality of communications bands includes signaling a first higher layer message to a user device in the first communications carrier, the first higher layer message including information regarding an activation of operations in a second communications carrier, coordinating with a second communications controller adapted for operations in the second communications carrier, an opportunistic transmission opportunity in the second communication carrier, generating a first physical layer message comprising an aperiodic trigger configured to prompt a channel measurement in accordance with a reference signal transmitted in the second communications carrier, the first physical layer message serving as an indication of the opportunistic transmission opportunity, and signaling the first physical layer message to the user device in the first communications carrier.