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. An apparatus 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 apparatus comprising:
a hybrid encoder for selecting for at least one relatively higher frequency transmit band, a spectrally compatible lower frequency gap in a transmit portion of the band plan;
an inverse discrete Fourier transform module for 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;
a hybrid upconverter for upconverting all time domain resultants to generate both base band images as well as replications thereof with an amount of the interpolation 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 for filtering out the undesired images, either baseband or higher frequency replications thereof and passing remaining mix onto the communication medium.
2. The apparatus for modulating and demodulating data of claim 1 , further comprising:
a hybrid downconverter for sampling received portions of the band plan including at least one relatively higher frequency received band at a rate which generates a spectral replication of the at least one received band at a relatively lower frequency range which overlaps with a gap in remaining received portions of the band plan; and
a discrete Fourier transform module for performing a time-to-frequency transform of the spectral replication of the at least one relatively higher frequency received band along with time-to-frequency transform of any remaining non selected received bands.
3. The apparatus for modulating and demodulating data of claim 1 , wherein the hybrid encoder further comprises:
an encoder for selecting for at least one relatively higher frequency transmit band, a spectrally compatible lower frequency gap in a transmit portion of the band plan; and
a spectral normalizer for reversing an Hermetian symmetry of the lower frequency image of the selected transmit band.
4. The apparatus for modulating and demodulating data of claim 1 , wherein the proscribed band plan exhibits a selected one of a 4.3125 kHz tone spacing and an 8.625 kHz tone spacing.
5. The apparatus for modulating and demodulating data of claim 1 , wherein the proscribed band plan comprises one of an International Telecommunications Union, ITU-T G.993 band plan and an American National Standards Institute Plan 998 band plan.
6. 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:
sampling received portions of the band plan including at least one relatively higher frequency received band at a rate which generates a spectral replication of the at least one received band at a relatively lower frequency range with overlaps with a gap in remaining received portions of the band plan;
performing a time-to-frequency transform of the spectral replication of the at least one relatively higher frequency received band along with time-to-frequency transform of any remaining non selected received bands;
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 all 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.
7. 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:
sampling received portions of the band plan including at least one relatively higher frequency received band at a rate which generates a spectral replication of the at least one received band at a relatively lower frequency range with overlaps with a gap in remaining received portions of the band plan;
performing a time-to-frequency transform of the spectral replication of the at least one relatively higher frequency received band along with time-to-frequency transform of any remaining non selected received bands; and
reversing Hermietian symmetry of the spectral replication of the at least one received band at the relatively lower frequency range.
8. The method of claim 7 , wherein the proscribed band plan exhibits a selected one of a 4.3125 kHz tone spacing and an 8.625 kHz tone spacing.
9. The method of claim 7 , wherein the proscribed band plan comprises one of an International Telecommunications Union, ITU-T G.993 band plan and an American National Standards Institute Plan 998 band plan.
10. An apparatus 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 apparatus comprising:
a hybrid downconverter for sampling received portions of the band plan including at least one relatively hither frequency received band at a rate which generates a spectral replication of the at least one received band at a relatively lower frequency range with overlaps with a gap in remaining received portions of the band plan;
a discrete Fourier transform module for performing a time-to-frequency transform of the spectral replication of the at least one relatively higher frequency received band along with time-to-frequency transform of any remaining non selected received bands;
a hybrid encoder for selecting for at least one relatively higher frequency transmit band, a spectrally compatible lower frequency gap in a transmit portion of the band plan;
an inverse discrete Fourier transform module for 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; and
a hybrid upconverter for upconverting all time domain resultants to generate both base band images as well as replications thereof with an amount of the interpolation 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 for filtering out the undesired images, either baseband or higher frequency replications thereof and passing remaining mix onto the communication medium.
11. An apparatus 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 apparatus comprising:
a hybrid downconverter for sampling received portions of the band plan including at least one relatively higher frequency received band at a rate which generates a spectral replication of the at least one received band at a relatively lower frequency range with overlaps with a gap in remaining received portions of the band plan;
a discrete Fourier transform module for performing a time-to-frequency transform of the spectral replication of the at least one relatively higher frequency received band along with time-to-frequency transform of any remaining non selected received bands; and
a hybrid decoder for reversing Hermetian symmetry of the spectral replication of the at least one received band at the relatively lower frequency range.
12. The apparatus for modulating and demodulating data of claim 11 , wherein the proscribed band plan exhibits a selected one of a 4.3125 kHz tone spacing and an 8.625 kHz tone spacing.
13. The apparatus for modulating and demodulating data of claim 11 wherein the proscribed band plan comprises one of an International Telecommunications Union ITU-T G.993 band plan and an American National Standards Institute Plan 998 band plan.