Patent ID: 7010027
Filing Date: 2006-03-07
Classification: H04L

Abstract:
1. 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.