Patent ID: 7254180

Claim:
A method for generating a discrete multitone signal comprising: modulating N carriers, corresponding to respective subchannels, in each sample period of the signal by performing an inverse discrete Fourier transform of N modulation symbols each of which symbols represents a signal point in a QAM constellation for a respective subchannel, said QAM constellation comprising a basic constellation of M≧2 m signal points where m is the number of data bits to be communicated over the subchannel in a said sample period; defining, for each of N c ≦N of said subchannels, an expanded QAM constellation comprising pM signal points including said basic constellation of points, where p is an integer greater than 1; defining, in each said expanded constellation, p−1 equivalent signal points for each signal point of the basic constellation, where each of the p−1 equivalent points is selected from redundant points in the opposite quadrant of the constellation to the corresponding point of the basic constellation; and, generating the discrete multitone signal in a said sample period by selecting, for each of said N c subchannels, the modulation symbol representing either a basic constellation point or a corresponding equivalent point such that the peak value of the signal does not exceed a predetermined threshold.