A method and apparatus of signaling radio resource allocation in a wireless communication system is disclosed. The method comprises: dividing the radio resource into units of a first type of assignment and of a second type; using the first type of assignment units for the first type of assignment; using the second type of assignment units for the second type of assignment; multiplexing the first type and the second type of assignments in the same frame; indicating the assignment for each of a plurality of mobile stations by a base station; determining the multiplexing mode by the base station; and communicating the multiplexing mode to each of the plurality of mobile stations by the base station.