TIME-DOMAIN EQUALIZATION FOR DISCRETE MULTI-TONE SYSTEMS
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Accused Products
Abstract
A multiple carrier communication system includes a primary impulse shortening filter that receives an output signal of an analog to digital converter and accepts coefficients. A secondary impulse shortening filter receives the output signal of the analog to digital converter, outputs an output signal, and passes coefficients to the primary impulse shortening filter. A reference signal generator outputs a reference signal. A comparator compares the output signal and the reference signal and outputs a resulting error signal. An adaptive processor computes coefficients for the secondary impulse shortening filter based on the error signal.
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Citations
75 Claims
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1-35. -35. (canceled)
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36. A multiple carrier communication system receiver for generating output data, the receiver comprising:
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a primary impulse shortening filter connected to receive a digital signal, accept a first set of coefficients, and output a primary digital signal; a delay connected to receive the digital signal and generate a delayed digital signal; a secondary impulse shortening filter connected to receive the delayed digital signal, accept a second set of coefficients, and output a secondary digital signal; a reference signal generator configured to output a reference signal; a comparator connected to compare the secondary digital signal and the reference signal and output a resulting error signal; and a processor that computes the second set of coefficients based on the error signal and copies the second set of coefficients to the primary impulse shortening filter as the first set of coefficients. - View Dependent Claims (37, 38, 39, 40, 41, 42)
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43. A method of simultaneously generating a first set of coefficients and generating output data in a system comprising a primary impulse shortening filter connected to receive a digital signal, accept the first set of coefficients, and output a primary digital signal and a secondary impulse shortening filter connected to receive a delayed digital signal, accept a second set of coefficients, and output a secondary digital signal, the method of generating the first set of coefficients comprising:
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delaying the digital signal to generate the delayed digital signal; generating a reference signal; comparing the secondary digital signal and the reference signal to generate an error signal; and computing the second set of coefficients based on the error signal and copying the second set of coefficients to the primary impulse shortening filter as the first set of coefficients; wherein the generating the first set of coefficients and the outputting a primary digital signal occur simultaneously. - View Dependent Claims (44, 45, 46)
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47. A method for transmitting information in a VDSL communication system comprising:
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selecting a cyclic prefix length from a plurality of candidate lengths based on respective bit rates obtained for the candidate lengths; and adding an end-portion of a block of information bits at a beginning of the block, wherein the added end-block portion has a length equal to the selected cyclic prefix length. - View Dependent Claims (48, 49, 50, 51, 52)
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53. A method of dynamically selecting a cyclic prefix length in a VDSL communication system, the method comprising:
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computing a respective maximum bit rate value for each of a plurality of candidate cyclic prefix lengths; identifying a particular one of the candidate cyclic prefix lengths having the largest maximum bit rate value of the computed maximum bit rate values; and adding an end-portion of a block of information bits at a beginning of the block, wherein the added end-block portion has a length equal to the particular one candidate cyclic prefix length. - View Dependent Claims (54, 55, 56, 57)
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58. A VDSL communication system comprising:
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a VDSL receiver comprising; logic that computes a bit rate value for each of a plurality of candidate cyclic prefix lengths; a transmitter that transmits the bit rate values; a VDSL transmitter comprising; a receiver that receives the bit rate values; logic that identifies a particular one of the candidate cyclic prefix lengths having the largest bit rate value of the computed bit rate values. - View Dependent Claims (59, 60)
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61. A method for adapting a primary impulse shortening filter in a VDSL communication system comprising a VDSL transmitter and VDSL receiver, the method comprising:
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selecting a first cyclic prefix length for the communication system from a set of candidate lengths; transmitting data having a cyclic prefix of the first selected length to the VDSL receiver; computing a first maximum bit rate value in the VDSL receiver for the first selected length; sending the first maximum bit rate value to the VDSL transmitter; selecting a second cyclic prefix length for the communication system from the set of candidate lengths; transmitting data having a cyclic prefix of the second selected length to the VDSL receiver; computing a second maximum bit rate value in the VDSL receiver for the second selected length; sending the second maximum bit rate value to the VDSL transmitter; comparing the first maximum bit rate value to the second maximum bit rate value; and selecting the cyclic prefix length corresponding to the greater of the first and second maximum bit rate values. - View Dependent Claims (62)
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63. A method for adapting an impulse shortening filter in a VDSL communication system having a spectrally constrained impulse shortening filter, the method comprising:
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scaling predetermined reference values with a set of scaling factors to form scaled values; applying an inverse discrete Fourier transform to the scaled values to form a reference signal; comparing an output signal of the spectrally constrained impulse shortening filter to the reference signal to compute an error signal; and computing coefficients of the spectrally constrained impulse shortening filter in an adaptive processor based on the error signal. - View Dependent Claims (64, 65)
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66. A method for adapting an impulse shortening filter in a VDSL communication system having a spectrally constrained impulse shortening filter, the method comprising:
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receiving a digital signal; applying the digital signal to the spectrally constrained impulse shortening filter to obtain a first output signal; computing a reference signal from the first output signal; delaying the digital signal to produce a delayed digital signal; applying the delayed digital signal to the spectrally constrained impulse shortening filter to obtain a second output signal; comparing the second output signal to the reference signal to compute an error signal; and computing coefficients of the spectrally constrained impulse shortening filter in an adaptive processor based on the error signal. - View Dependent Claims (67, 68, 69, 70, 71, 72, 73)
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74. A VDSL communication system comprising:
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a spectrally constrained impulse shortening filter connected to receive a digital signal and to accept coefficients, a reference signal generator configured to output a reference signal; a memory to store the reference signal as a predetermined signal; a discrete Fourier transform connected to receive the reference signal from the memory; a scaling filter connected to scale the reference signal using a set of scaling factors; an inverse discrete Fourier transform connected to receive the scaled reference signal; a comparator connected to compare the digital signal and the scaled reference signal and to output a resulting error signal; and an adaptive processor that computes coefficients for the spectrally constrained impulse shortening filter based on the error signal. - View Dependent Claims (75)
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Specification