A method is provided for specifying a transmission mode for each signal portion of a multi-carrier signal transmitted between a first device and a second device. The method includes defining an adaptive modulation and coding (AMC) set divided into a plurality of subsets wherein each of the plurality of subsets includes a plurality of transmission modes for transmission of a signal portion. The method further includes selecting a transmission mode subset from the plurality of subsets for transmission of the multi-carrier signal from a first device to a second device, selecting a signal portion transmission mode for each signal portion from the plurality of transmission modes of the selected transmission mode subset, defining semantic bits that indicate the selected transmission mode subset, defining an indicator bit for each signal portion indicating the selected sub-carrier transmission mode, and transmitting the semantic bits and the indicator bit for each signal portion from a first device to a second device.