Method and apparatus for adaptive PCM level estimation and constellation training
AssigneePCTEL, Inc.
InventorsXuming Zhang, Sverrir Olafsson
Life of this patent
Estimating the term…
Abstract
Systems compensate for the presence of digital impairments using adaptive constellation techniques. Sample magnitudes are estimated from received samples transmitted during a training period using an algorithm based on minimizing the sum of squares of the estimated errors, after which a suitable constellation is derived. In one embodiment, an optimum least-squares algorithm is employed. In an alternate embodiment, a least mean squares (LMS) or normalized LMS algorithm is performed.
Claims20
A method of creating a constellation for use by a first modem to compensate for digital impairments in a communication channel between said first modem and a second modem, said method comprising:
- training an equalizer having a feedforward portion and a feedback portion to yield feedforward and feedback tap values;
- receiving an analog representation of a digital impairment learning (DIL) by said first modem via said communication channel, said DIL including a plurality of segments, each of said plurality of segments being characterized by a PCM level, a PCM reference and a sign pattern;
- converting said analog representation of said DIL to generate a digital representation of said DIL;
- equalizing said digital representation of said DIL, using said equalizer, to generate equalized segments;
- arranging said equalized segments into a sequence of signal vectors;
- selecting level estimates to minimize a sum of squared errors, wherein said errors are based on differences between said signal vectors and a product of said feedforward and feedback tap values, values of said sign pattern and said level estimates;
- and
- defining a constellation based on said estimated sample magnitudes.
A modem capable of creating a constellation compensating for digital impairments in a communication channel between said modem and a remote device, said modem comprising:
- a receiver configured to receive an analog representation of a digital impairment learning (DIL) via said communication channel, said DIL including a plurality of digital symbols, wherein said plurality of segments, each of said plurality of segments being characterized by a PCM level, a PCM reference and a sign pattern;
- an analog to digital converter configured to convert said analog representation of said DIL to generate a digital representation of said DIL;
- and
- an equalizer configured to equalize said digital representation of said DIL obtained from said converter to generate equalized segments, said equalizer having a feedforward portion and a feedback portion, wherein said equalizer is trained, prior to said receiver receiving said analog representation of a training sequence, to yield feedforward and feedback tap values;
- wherein said modem arranges said equalized segments into a sequence of signal vectors, selected level estimates to minimize a sum of squared errors, wherein said errors are based on differences between said signal vectors and a product of said feedforward and feedback tap values, values of said sign pattern and said level estimates, and wherein said modem defines a constellation based on said estimated sample magnitudes.
A method of creating a constellation for use by a first modem to compensate for digital impairments in a communication channel between said first modem and a second modem, said method comprising:
- training an equalizer having a feedforward portion and a feedback portion to yield feedforward and feedback tap values;
- receiving an analog representation of a digital impairment learning (DIL) by said first modem via said communication channel, said DIL including a plurality of segments, each of said plurality of segments being characterized by a PCM level, a PCM reference and a sign pattern;
- converting said analog representation of said DIL to generate a digital representation of said DIL;
- equalizing said digital representation of said DIL, using said equalizer, to generate equalized segments;
- arranging said equalized segments into a sequence of signal vectors;
- selecting level estimates to minimize a sum of squared errors, wherein said errors are based on differences between said signal vectors and a product of said feedforward and feedback tap values, values of said sign pattern, said level estimates and error values, wherein said error values are based on differences between said signal vectors and a product of said feedforward and feedback tap values, values of said sign pattern and previous or current said level estimates;
- and
- defining a constellation based on said estimated sample magnitudes.
A modem capable of creating a constellation compensating for digital impairments in a communication channel between said modem and a remote device, said modem comprising:
- a receiver configured to receive an analog representation of a digital impairment learning (DIL) by said first modem via said communication channel, said DIL including a plurality of digital symbols, wherein said plurality of segments, each of said plurality of segments being characterized by a PCM level, a PCM reference and a sign pattern;
- an analog to digital converter configured to convert said analog representation of said DIL to generate a digital representation of said DIL;
- and
- an equalizer configured to equalize said digital representation of said DIL obtained from said converter to generate equalized segments, said equalizer having a feedforward portion and a feedback portion, wherein said equalizer is trained, prior to said receiver receiving said analog representation of a training sequence, to yield feedforward and feedback tap values;
- wherein said modem arranges said equalized segments into a sequence of signal vectors, selects level estimates to minimize a sum of squared errors, wherein said errors are based on differences between said signal vectors and a product of said feedforward and feedback tap values, values of said sign pattern, said level estimates and error values, wherein said error values are based on differences between said signal vectors and a product of said feedforward and feedback tap values, values of said sign pattern and previous or current said level estimates, and wherein said modem defines a constellation based on said estimated sample magnitudes.
Dependencies are inferred from the claim text.