Multistandard discrete multi-tone (DMT) digital subscriber line (DSL) system

A digital subscriber line transmission system using QAM modulation on N=4096/p tones spaced by 4.3125 kHz wherein p and q are powers of 2 (p=1, 2, 4, 8, . . . ;

• q=1, 2, 4, 8, . . . ), including at least two operating modes:
• a VDSL standard operating mode where all N tones are used to convey significant values;
• and
• an ADSL standard operating mode where only the first n among the N tones are used to convey significant values;
• comprising, on the transmitter side:
• an inverse fast Fourier transform circuit having N frequency domain value inputs corresponding to said tones, among which only the first receive values corresponding to the n used tones, the remaining inputs being zeroed,
• a decimator providing one sample for every r samples output by the inverse fast Fourier transform circuit, with r=N/n,
• a digital-to-analog converter coupled between the decimator and a subscriber line;
• comprising, on the receiver side:
• an analog-to-digital converter sampling the signal on the subscriber line at a frequency F/r, where F is the operating frequency of the inverse fast Fourier transform circuit;
• an interpolator generating samples at frequency F from the samples provided by the analog-to-digital converter;
• and
• a fast Fourier transform circuit operating at frequency F and receiving the samples from the interpolator through a time domain equalizer;
• wherein, when all N tones are used, the time domain equalizer is bypassed.