Method and apparatus for extending the frequency range of multi-tone modems

摘要

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.