Multimode modulation and coding of QAM

A general-purpose modulation and coding implementation that is based on the quadrature amplitude modulation (QAM) family of modulation is described. The technique utilizes the 'superposed' property of certain rectangular QAM constellations, along with the fact that optimal four-state trellis codes for such constellations are essentially identical, to provide a single modem architecture capable of performing over a wide range of power and bandwidth efficient transmission using either an uncoded or a coded modulation scheme. While the specific modulation and coding techniques are not new, the authors believe that their intrinsic compatibility is not well known and provides attractive system flexibility.<
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