Patent ID: 7274653

Claim:
A QAM transmitting system, comprising: a source of a level 1 and a level 2 data stream, each data stream carrying successive symbols; and a hierarchical QAM transmitter, coupled to the level 1 and level 2 data stream source, for generating a hierarchical QAM signal in which a level 1 symbol is represented by a data point in one of four quadrants in the I-Q plane, and a level 2 symbol is represented by the data point in one of four sub-quadrants surrounding a center point of the quadrant containing the level 1 data point, wherein the level 2 data point is spaced away from the center point by a grouping factor; wherein the QAM transmitter comprises: a level 1 QPSK modulator, responsive to the level 1 data stream, for generating a level 1 QPSK signal representing the level 1 symbol; and a level 2 QPSK modulator, responsive to the level 2 data stream for generating a level 2 QPSK signal representing the level 2 symbol; the system wherein: a QAM signal generator, for weighting the level 1 QPSK signal by a factor of 1, weighting the level 2 QPSK signal by the grouping factor, and combining the weighted level 1 and level 2 QPSK signals to generate the hierarchical QAM signal, the QAM signal generator comprising: a variable gain amplifier, having a gain set to the grouping factor, for generating the weighted level 2 QPSK signal; and a signal combiner, for combining the level 1 QPSK signal and the weighted level 2 QPSK signal; and by the grouping factor being set to more closely match the bit error rate performance of the level 1 and level 2 data streams.