# US 7,613,238 B2 · Apparatus and method for decision error compensation in an adaptive equalizer

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- Number: US 7,613,238 B2
- Document ID: US7613238B2
- Status: Granted
- Kind: B2
- Application number: 11/225,636
- Filed: 2005-09-13
- Published: 2007-03-15
- Granted: 2009-11-03
- Earliest claimed: 2005-09-13
- Assignees: Mediatek Inc.
- Inventors: Chiao-Chih Chang
- Web page: https://patentgrep.com/patent/US7613238B2

## CPC

- H04L 25/03057: {with a recursive structure (H04L25/03031 takes precedence)}
- H04L 1/0047: {Decoding adapted to other signal detection operation (in conjunction with sequence estimation or equalization H04L25/03286)}
- H04L 1/0059: {Convolutional codes}
- H04L 1/0065: {Serial concatenated codes}
- H04L 2025/0349: {as a feedback filter}
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

An adaptive equalizer comprises: a forward equalizer (FE) receiving a symbol stream to generate an FE output; a decision feedback equalizer (DFE) receiving a decision symbol stream to generate a DFE output; a first adder, coupled to the forward equalizer and the decision feedback equalizer, adding the FE and DFE outputs to generate an equalizer output; a first trellis decoder, coupled to the first adder, receiving the equalizer output to generate a trellis decoded stream by a trellis decoding process; and a compensator for compensating the equalizer output according to the decision symbol stream, the trellis decoded stream, and a coefficient vector stored in the decision feedback equalizer, to generate a compensated equalizer output.

## Claims

### Claim 1

An adaptive equalizer with decision error compensation, comprising:
a forward equalizer (FE), receiving a symbol stream to generate an FE output;
a decision feedback equalizer (DFE), receiving a decision symbol stream to generate a DFE output, wherein the decision symbol stream is an estimation of the symbol stream;
a first adder, adding the FE and DFE outputs to generate an equalizer output;
a first trellis decoder, receiving the equalizer output to generate a trellis decoded stream by a trellis decoding process; and
a compensator for compensating the equalizer output according to the decision symbol stream, the trellis decoded stream, and a coefficient vector stored in the decision feedback equalizer, to generate a compensated equalizer output, wherein the compensator comprises:
a first delay unit, receiving the equalizer output and delaying the equalizer output for a time m;
a second delay unit, receiving the decision symbol stream and delaying the decision symbol stream for the time m;
a comparator, generating an error signal by comparing the trellis decoded stream and the delayed decision symbol stream;
an FIR array, generating a summation from the multiplication of the coefficient vector and the error signal; and
a second adder, adding the delayed equalizer output and the summation to generate the compensated equalizer output.

### Claim 2 (depends on 1)

The adaptive equalizer as claimed in claim 1, wherein the FIR array comprises:
a multiplexer, receiving the coefficient vector;
a plurality of tap cells coupled in series to delay the error signal sequentially;
a plurality of multipliers, each coupled to the multiplexer and a corresponding tap cells, multiplying a delayed error signal and one coefficient;
an accumulator for adding the multiplication results to generate the summation.

### Claim 3 (depends on 2)

The adaptive equalizer as claimed in claim 2, wherein the multiplexer comprises a selector processing the coefficient vector before being output to the multipliers by:
outputting a coefficient to a corresponding tap cell if the coefficient exceeds a threshold or the adjacent coefficient exceeds a threshold; and
omitting a coefficient if neither the coefficient nor the adjacent coefficient exceeds the threshold.

### Claim 4 (depends on 2)

The adaptive equalizer as claimed in claim 2, wherein the multiplexer comprises:
a controller, periodically delivering a control signal; and
a buffer for storing the coefficient vector; wherein
when the control signal is delivered, the buffer is updated with the current coefficient vector from the decision feedback equalizer.

### Claim 5

An equalization method for generating an equalizer output from a symbol stream and compensating a decision error thereof, comprising:
performing a forward equalization (FE) on the symbol stream to generate an FE output;
estimating the equalizer output to generate a decision symbol stream;
performing a decision feedback equalization (DFE) on the decision symbol stream to generate a DFE output;
adding the FE and DFE outputs to generate the equalizer output;
trellis decoding the equalizer output to generate a trellis decoded stream; and
compensating the equalizer output according to the decision symbol stream, the trellis decoded stream, and a coefficient vector corresponding to the decision feedback equalization, to generate a compensated equalizer output, wherein the compensation comprises:
delaying the equalizer output for a time m;
delaying the decision symbol stream for the time m;
comparing the trellis decoded stream and the delayed decision symbol stream to generate an error signal;
summing the multiplication of the coefficient vector and the error signal; and
adding the delayed equalizer output and the summation to generate the compensated equalizer output.

### Claim 6 (depends on 5)

The equalization method as claimed in claim 5, wherein the compensation further comprises:
delaying the error signal to generate a plurality of delayed error signals;
multiplying each delayed error signal and a corresponding coefficient;
summing all the multiplications to generate the summation.

### Claim 7 (depends on 6)

The equalization method as claimed in claim 6, wherein the multiplication further comprises:
multiplying a coefficient and a corresponding delayed error signal if the coefficient or adjacent coefficients exceed a threshold; and
skipping the multiplication if neither the coefficient nor the adjacent coefficients exceed the threshold.

### Claim 8 (depends on 6)

The equalization method as claimed in claim 6, wherein the coefficient vector stored in the buffer is updated periodically with the decision feedback equalization.