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