Spectrally constrained impulse shortening filter for a discrete multi-tone receiver
View Patent ↗A channel in a multiple carrier communication system is equalized by computing a target spectral response, shortening the impulse response of the channel so that a significant part of an energy of the impulse response is confined to a region that is shorter than a target length and filtering the signal based on the target spectral response.
1. A spectrally constrained impulse shortening filter for a multiple carrier communication system, the system being configured to receive a signal and including a channel that has an impulse response, the filter comprising:
an input connected to receive the signal;
a digital structure, coupled to the input, configured to select an impulse response, wherein the digital structure is operable to (1) measure received noise power spectral density, (2) compute a cost function using the noise power, the cost function being dependent on the impulse response, (3) reduce the dimensionality of a space over which the cost function is defined and (4) minimize the cost function.
2. The filter of claim 1 wherein the digital structure comprises a discrete Fourier transform and the noise power spectral density is measured at an output of the discrete Fourier transform.
3. A spectrally constrained impulse shortening filter for a multiple carrier communication system, the system being configured to receive a signal and including a channel that has an impulse response, the filter comprising:
an input connected to receive the signal;
a digital structure, coupled to the input, for equalizing a channel, wherein the digital structure is configured to (1) measure received noise power spectral density, (2) compute a target spectral response having a magnitude constraint that is based on the measured noise power spectral density and (3) select a frequency response of the spectrally constrained impulse shortening filter based on the target spectral response.
4. The filter of claim 3 wherein the digital structure comprises a discrete Fourier transform and the noise power spectral density is measured at an output of the discrete Fourier transform.
5. A receiver for receiving a multiple carrier signal from a communication channel having an impulse response, the receiver comprising:
an analog-to-digital converter connected to receive the signal from the communication channel; and
a spectrally constrained impulse shortening filter connected to receive the signal from the analog-to-digital converter and configured to (1) measure received noise power spectral density, (2) compute a cost function using the noise power, the cost function being dependent on the impulse response, (3) reduce the dimensionality of a space over which the cost function is defined and (4) minimize the cost function;
wherein the spectrally constrained impulse shortening filter comprises a discrete Fourier transform connected to receive the output of the spectrally constrained impulse shortening filter and a decoder connected to receive outputs of the discrete Fourier transform.
6. The receiver of claim 5 , wherein the noise power spectral density is measured at an output of the discrete Fourier transform.
7. A receiver for receiving a multiple carrier signal from a communication channel having an impulse response, the receiver comprising:
an analog-to-digital converter connected to receive the signal from the communication channel; and
a spectrally constrained impulse shortening filter connected to receive the signal from the analog-to-digital converter and configured to (1) measure received noise power spectral density, (2) compute a target spectral response having a magnitude constraint that is based on the measured noise power spectral density and (3) select a frequency response of the spectrally constrained impulse shortening filter based on the target spectral response;
a discrete Fourier transform connected to receive the output of the spectrally constrained impulse shortening filter and a decoder connected to receive outputs of the discrete Fourier transform.
8. The receiver of claim 7 , wherein the target spectral response is computed from measured noise power spectral density.
9. The receiver of claim 7 , wherein the noise power spectral density is measured at an output of the discrete Fourier transform.
10. The receiver of claim 7 , wherein the target spectral response is approximated by the inverse of the measured noise power spectral density.
11. A modem comprising:
an encoder connected to receive digital data and configured to output a constellation of complex values;
an inverse discrete Fourier transform connected to receive the constellation from the encoder;
a digital-to-analog converter connected to the inverse discrete Fourier transform and configured to output a signal to a communication channel;
an analog-to-digital converter configured to receive the signal from the communication channel;
a spectrally constrained impulse shortening filter configured to (1) measure received noise power spectral density, (2) compute a cost function using the noise power, the cost function being dependent on the impulse response, (3) reduce the dimensionality of a space over which the cost function is defined and (4) minimize the cost function;
a discrete Fourier transform connected to receive an output of the spectrally constrained impulse shortening filter; and
a decoder connected to the discrete Fourier transform and configured to output digital data.
12. The modem of claim 11 , wherein the noise power spectral density is measured at an output of the discrete Fourier transform.
13. A modem comprising:
an encoder connected to receive digital data and configured to output a constellation of complex values;
an inverse discrete Fourier transform connected to receive the constellation from the encoder;
a digital-to-analog converter connected to the inverse discrete Fourier transform and configured to output a signal to a communication channel;
an analog-to-digital converter configured to receive the signal from the communication channel;
a spectrally constrained impulse shortening filter configured to (1) measure received noise power spectral density, (2) compute a target spectral response having a magnitude constraint that is based on the measured noise power spectral density and (3) select a frequency response of the spectrally constrained impulse shortening filter based on the target spectral response;
a discrete Fourier transform connected to receive an output of the spectrally constrained impulse shortening filter; and
a decoder connected to the discrete Fourier transform and configured to output digital data.
14. The modem of claim 13 , wherein the noise power spectral density is measured at an output of the discrete Fourier transform.