1. A method for space-time encoding multicarrier signals performed by a multicarrier transceiver, the method comprising: linearly transforming input symbols of a constellation set with a selected transformation matrix to generate linearly transformed symbols; forming a complex symbol for each of a plurality of transmit antennas from the linearly transformed symbols; forming code matrices from the complex symbols; and generating a quasi-orthogonal space-time matrix from the code matrices for use in generating multicarrier signals for transmission by the transmit antennas, wherein the linearly transforming, the forming of complex symbols, the forming of code matrices and the generating is performed by a space-time encoder of the multicarrier transceiver.