Method and apparatus for extending the frequency range of multi-tone modems
View Patent ↗An inverse discrete Fourier transform (IDFT) processor processing a lower frequency image of a selected transmit band along with base images of remaining transmit bands called for in a corresponding X-DSL standard. A hybrid upconverter processing the IDFT output by generating a higher frequency replication of the imaged transmit band falling in the standards based frequency range along with the base band images of remaining transmit bands and selectively passing onto the communication medium only images or replications called for by the standards. A hybrid downconverter processing at least one of the received bands at sampling rates below Nyquist thereby creating a lower frequency image within the range of a discrete Fourier transform (DFT) processor. The hybrid downconverter clears the frequency band in which the image processed at sub-Nyquist rates will fold. The DFT then transforms only the images or replications falling within its frequency range.
1. A method for modulating and demodulating data on a communication medium in accordance with a proscribed band plan including frequency division multiplexed transmit and receive bands; and the method comprising:
selecting for at least one relatively higher frequency transmit band, a spectrally compatible lower frequency gap in a transmit portion of the band plan;
performing a frequency-to-time transform of a lower frequency image of the selected transmit band concurrently with frequency-to-time transforms of any remaining non-selected transmit bands;
upconverting time domain resultants to generate both base band images as well as replications thereof with an amount of the upconversion required determined by a requirement that the transformed image of the selected transmit band overlap with the selected transmit band on the communication medium; and
filtering out the undesired images, either baseband or higher frequency replications thereof and passing remaining mix onto the communication medium.