Apparatus and method for stable DEF using selective FBF

• US 20070133672A1
• Filed: 12/06/2006
• Published: 06/14/2007
• Est. Priority Date: 12/09/2005
• Status: Active Grant

• Current Assignee: Electronics and Telecommunications Research Institute
• Original Assignee: Electronics and Telecommunications Research Institute
• Inventors: Kwon, O-Hyung, Lee, Soo-In, Lee, Jae-Ho
• Granted Patent: US 7,944,964 B2
• Time in Patent Office: Days
• US Class Current: 375/233
• CPC Class Codes: H04L 2025/0349 as a feedback filter
• CPC Class Codes: H04L 2025/0363 Feature restoration, e.g. constant modulus
• CPC Class Codes: H04L 2025/03656 Initialisation
• CPC Class Codes: H04L 2025/03687 of step size
• CPC Class Codes: H04L 2025/037 Detection of convergence state
• CPC Class Codes: H04L 25/0307 using blind adaptation

Abstract

A decision feedback equalizing apparatus selectively using a feedback filter and a method thereof are provided. The apparatus includes: an equalizing unit including a feed forward filter (FFF) for correcting a distorted transmission channel by receiving a match-filtered signal and a feedback filter (FBF) for reducing inter symbol interference ISI of the corrected transmission channel for driving only the FFF in a blind mode and driving the FFF and the FBF in a decision directed mode; a diverge/converge determining unit for determining whether the decision feedback equalizing apparatus is diverged or converged using a unit square error obtained through a least unit square algorithm; and a filter controlling unit for controlling the equalizing unit in a blind mode if the decision feedback equalizing apparatus is determined as divergence, and for controlling the equalizing unit in a decision directed mode if the decision feedback equalizing apparatus is determined as convergence.

Claims

1. A decision feedback equalizing apparatus selectively using a feedback filter comprising:

an equalizing means including a feed forward filter (FFF) for correcting a distorted transmission channel by receiving a match-filtered signal and a feedback filter (FBF) for reducing an inter symbol interference (ISI) of the corrected transmission channel for driving only the FFF in a blind mode and driving the FFF and the FBF in a decision directed mode;

a diverge/converge determining means for determining whether the decision feedback equalizing apparatus is diverged or converged using a means square error (MSE) obtained through a least means square (LMS) algorithm; and

a filter controlling means for controlling the equalizing means in a blind mode if the decision feedback equalizing apparatus is determined as divergence, and for controlling the equalizing means in a decision directed mode if the decision feedback equalizing apparatus is determined as convergence.

2. The decision feedback equalizing apparatus as recited in claim 1, wherein the equalizing means includes:

a feed forward filter for receiving a match-filtered signal and filtering the received signal to correct a distorted transmission channel using the input match-filtered signal and error values differently inputted according to the blind mode and the decision directed mode;

a feedback filter for receiving an output signal of a slicer in the decision directed mode, and filtering the output signal to reduce the ISI of the corrected transmission channel;

a subtracting means for subtracting a filtering signal of the FFF and a filtering signal of the FBF; and

a down sampling means for down-sampling the subtracted signal to a symbol speed and outputs an equalizing signal.

3. The decision feedback equalizing apparatus as recited in claim 1, wherein the diverge/converge determining means includes:

a slicing means for creating a slicer output signal by receiving an outputs signal from the down sampling means, and calculating a second error value by subtracting the created slicer output signal from the output signal;

a mean square error calculating means for calculating a mean square error value using the LMS algorithm with the second error value;

a first threshold comparing means for controlling to reduce a step size and initializing a tab coefficient by determining it as divergence if the mean square error value is larger than the first threshold value;

a second threshold comparing means for setting a counter value to 0 by determining it as divergence if the mean square value is smaller than the first threshold value and larger than a second threshold value;

a counter calculating means for increasing the counter value by one if the mean square error value is smaller than the second threshold value; and

a third threshold comparing means for restoring the counter value to 0 and determining it as divergence if the increased counter value is smaller than a third threshold value, and determining it as convergence if the increased counter value is larger than the third threshold value.

4. The decision feedback equalizing apparatus as recited in claim 3, wherein the filter controlling means includes:

a multi-coefficient generating means for generating a first error value using a multi-modulus algorithm by receiving the output signal;

a first multiplexing means inputting 0 to the feedback filter to drive the equalizing means in a blind mode if the diverge/converge determining means determines as divergence, and inputting the slicer output to the feedback filter to drive the equalizing means in a decision directed mode if the diverge/converge determining means determines as convergence;

a second multiplexing means for outputting the first error value to drive the equalizing means in a blind mode if the divergence is determined, and outputting the second error value if the convergence is determined;

a third multiplexing means for outputting a first step side if the divergence is determined and outputting as second step size if the convergence is determined; and

a multiplying means for multiplying the second step size from the third multiplexing means and the output value of the second multiplexing means.

5. The decision feedback equalizing apparatus as recited in claim 4, wherein the multi-coefficient generating means generates the first error value using equation:

err_—

b(n)=real(y(n))×

(R_MMA²−

|real(y(n)) |²)(R _MMA=0.9382) +j*imag(y(n))×

(R_MMA²−

|imag(y(n))|²)

wherein err_b(n) denotes a first error value, and y(n) denotes an output signal.

6. The decision feedback equalizing apparatus as recited in claim 5, wherein the mean square error calculating means calculates the mean square error value using following equations:

7. An equalizing method applied to a decision feedback equalizing apparatus including a feed forward filter and a feedback filter comprising the steps of:

a) performing an equalization using only the feed forward filter at an initial stage;

b) determining whether the decision feedback equalizing apparatus is diverged or converged using a means square error (MSE) obtained through a least means square (LMS) algorithm for the equalization result from the step a);

c) performing a blind equalization that drives the feed forward filter only if the divergence is determined at the step b) and performing the step b) for determining whether the decision feedback equalizing apparatus is diverged or converged for the blind equalization result; and

d) performing a decision directed equalization that drives the feed forward filter and the feedback filter if the convergence is determined at the step b), and performing the step b) for determined whether the decision feedback equalizing apparatus is diverged or converged.

8. The method as recited in claim 7, wherein the step b) includes the steps of:

b-1) calculating a first error value using a multi-modulus algorithm with an output signal of the feed forward filter, creating a slicer output signal by slicing an output signal of the feed forward filter, calculating a second error value using the created slicer output signal, and calculating a mean square error value using the LMS algorithm with the second error value;

b-2) reducing a step size and initializing a tab coefficient by determining it as divergence if the mean square error value is larger than the first threshold value;

b-3) setting a counter value to 0 by determining it as divergence if the mean square value is smaller than the first threshold value and larger than a second threshold value;

b-4) increasing a counter value by one if the mean square error value is smaller than the second threshold value; and

b-5) determining it as divergence by restoring the counter value to 0 if the increased counter value is smaller than a third threshold value, and determining it as convergence if the increased counter value is larger than the third threshold value.

9. The method as recited in claim 7, wherein the filtering controlling step includes the steps of:

controlling to input 0 to the feedback filter to drive the decision feedback equalizing apparatus in a blind mode if a divergence is determined in the step b) and inputting the slicer output to the feedback filter to drive the decision feedback equalizing apparatus in a decision directed mode if a convergence is determined; and

controlling the decision feedback equalizing apparatus in a blind mode using the first error value and the first step size according to a multi-modulus algorithm if the divergence is determined, and controlling the decision feedback equalizing apparatus in a decision directed mode using the second error value and the second step size if the convergence is determined.