Method and apparatus for equalizing a digital signal received via multiple transmission paths

• US 6,526,093 B1
• Filed: 03/04/1999
• Issued: 02/25/2003
• Est. Priority Date: 03/04/1999
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Electric Research Laboratories, Inc. (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Electric Research Laboratories, Inc. (Mitsubishi Electric Corporation)
• Inventors: De, Parthapratim, Bao, Jay, Poon, Tommy C.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Fan, Chieh M.
• Application Number:
  US09/262,377
• Time in Patent Office: 1,454 Days
• Field of Search: 375/229, 375/230, 375/231, 375/232, 375/233, 375/240-2-2, 375/346, 375/349, 375/350, 708/322, 708/323, 333/18
• US Class Current: 375/233
• CPC Class Codes: H04L 2025/03382 Single of vestigal sideband
• CPC Class Codes: H04L 2025/0342 QAM
• CPC Class Codes: H04L 2025/0349 as a feedback filter
• CPC Class Codes: H04L 2025/03694 Stop and go
• CPC Class Codes: H04L 25/03057 with a recursive structure H04L25/03031 takes precedence
• CPC Class Codes: H04L 25/03987 Equalisation for sparse channels

Abstract

In a receiver, an adaptive decision feedback equalizer receives broadcast signals having multipath interference. The equalizer includes a feed-forward, a feedback, and a partial feedback forward filter. The equalizer also includes a slicer and two accumulators. An output from the slicer is processed by the feedback filter and the partial feedback filter. The output from the feedback filter is subtracted from output of the feed-forward filter to form the input to the slicer, and the output of the partial feedback filter is subtracted from the received signal to form the input for the feed-forward filter to reduce the multipath interference.

Claims

1. In a receiver, an adaptive decision feedback equalizer for equalizing a received digital broadcast signal including multipath interference, comprising;

a slicer;

a feedback filter;

a partial feedback filter;

a feed-forward filter connected to each other so that an output from the slicer is processed by the feedback filter and the partial feedback filter, and an output from the feedback filter is subtracted from an output of the feed-forward filter to form an input to the slicer, and an output of the partial feedback filter is subtracted from the received signal to form an input to the feed-forward filter to reduce the multipath interference, and wherein each of the feedback filter, the partial feedback filter and the feed-forward filter includes a plurality of taps having associated coefficients;

means for only updating any taps of the plurality of taps of each of the feedback filter, the partial feedback filter and the feed-forward filter having a measured energy level above a predetermined threshold; and

means for only updating taps adjacent to any taps of the plurality of taps of each of the feedback filter, the partial feedback filter and the feed-forward filter having a measured energy level above the the predetermined threshold.

2. The equalizer of claim 1 further comprising:

means for measuring an energy level at each tap of the feed-forward filter and each tap of the feedback filter; and

means for multiplying a step size of a coefficient at each tap of the feed-forward and the feedback filter by a weight parameter w, where w is one when the measured energy level is above a predetermined level, and w is zero otherwise.

3. The equalizer of claim 2 wherein only coefficients of taps having the weight parameter w equal to one are updated.

4. The equalizer of claim 1 wherein the receiver is a digital television receiver.

5. The equalizer of claim 1 wherein the receiver is a cable receiver.

6. In a receiver, a method for adaptively equalizing a received digital broadcast signal including multipath interference, comprising the steps of:

filtering an output from a slicer by a feedback filter and a partial feedback filter;

subtracting an output from the feedback filter from an output of a feed-forward filter to form an input to the slicer;

subtracting an output from the partial feedback filter from the received signal to form an input to the feed-forward filter to reduce the multipath interference

measuring an energy level at each tap of the feed-forward filter and each tap of the feedback filter; and

multiplying a step size of a coefficient at each tap of the feed-forward and the feedback filter by a weight parameter w, where w is one when the measured energy level is above a predetermined level, and w is zero otherwise.

7. The method of claim 6 wherein only coefficients of taps having the weight parameter w equal to one are updated.

8. In a receiver, a method for adaptively equalizing a received digital broadcast signal including multipath interference, comprising the steps of:

measuring an energy level at each tap of a feed-forward filter and each tap of a feedback filter of an equalizer;

multiplying a step size of a coefficient at each tap of the feed-forward and the feedback filter by a weight parameter w, where w is one when the measured energy level is above a predetermined level, and w is zero otherwise; and

accepting a main digital signal at taps of the feed-forward and the feedback filter having an energy level above the predetermined level, and rejecting ghost digital signals at all other taps.

9. The method of claim 8 wherein only coefficients of taps of the feed-forward and the feedback filter having the weight parameter w equal to one are updated.

10. In a receiver, an adaptive decision feedback equalizer for equalizing a received digital broadcast signal including multipath interference, comprising;

a slicer;

a feedback filter including a plurality of taps having associated coefficients, and means for only updating taps having a measured energy level above a predetermined threshold;

a partial feedback filter including a plurality of taps having associated coefficients, and means for only updating taps having a measured energy level above a predetermined threshold;

a feed-forward filter including a plurality of taps having associated coefficients, and means for only updating taps having a measured energy level above a predetermined threshold, the filters connected to each other so that an output from the slicer is processed by the feedback filter and the partial feedback filter, and an output from the feedback filter is subtracted from an output of the feed-forward filter to form an input to the slicer, and an output of the partial feedback filter is subtracted from the received signal to form an input to the feed-forward filter to reduce the multipath interference; and

means for only updating taps of any of the filters adjacent to the taps of any of the filters having a measured energy level above the predetermined threshold.