Method and apparatus for pipelined joint equalization and decoding for gigabit communications

• US 7,913,154 B2
• Filed: 02/28/2008
• Issued: 03/22/2011
• Est. Priority Date: 11/03/2000
• Status: Active Grant

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.)
• Original Assignee: Agere Systems Incorporated (Broadcom, Inc.)
• Inventors: Azadet, Kameran, Haratsch, Erich Franz
• Primary Examiner(s): Torres; Joseph D
• Application Number:
  US12/039,474
• Publication Number:
  US 20080317179A1
• Time in Patent Office: 1,118 Days
• Field of Search: 714794-796, 375/262
• US Class Current: 714/794
• CPC Class Codes: H03M 13/03 Error detection or forward error correction by redundancy in data representation, i.e. code words containing more digits than the source words
• CPC Class Codes: H03M 13/6331 Error control coding in combination with equalisation
• CPC Class Codes: H04L 25/03057 with a recursive structure H04L25/03031 takes precedence
• CPC Class Codes: H04L 25/03235 with state-reduction using feedback filtering
• CPC Class Codes: H04L 25/4917 using multilevel codes

Abstract

A method and apparatus for the implementation of reduced state sequence estimation is disclosed, with an increased throughput using precomputation (look-ahead), with only a linear increase in hardware complexity with respect to the look-ahead depth. The present invention limits the increase in hardware complexity by taking advantage of past decisions (or survivor symbols). The critical path of a conventional RSSE implementation is broken up into at least two smaller critical paths using pipeline registers. Various reduced state sequence estimation implementations are disclosed that employ one-step or multiple-step look-ahead techniques to process a signal received from a dispersive channel having a channel memory.

Claims

1. A method for processing a signal received from a dispersive channel using a reduced-state sequence estimation technique, said channel having a channel impulse response, said method comprising the steps of:

precomputing partial intersymbol interference estimates for each of a plurality of postcursor taps of said channel impulse response, wherein said precomputed partial intersymbol interference estimates are based on each possible value for a data symbol;

selecting a precomputed partial intersymbol interference estimate for each of said plurality of postcursor taps based on a past decision from a corresponding state, wherein a selected partial intersymbol interference estimate for a first postcursor tap is a selected intersymbol interference estimate;

computing a branch metric based on said selected intersymbol interference estimate;

computing a new path metric for a path extension from a corresponding state based on said branch metric; and

determining a best survivor path into a state by selecting a path having a best new path metric among said corresponding computed new path metrics.

2. The method of claim 1, wherein said first selecting step comprises the step of selecting a precomputed partial intersymbol interference estimate for a group of said plurality of postcursor taps based on past decisions, wherein a selected partial intersymbol interference estimate for a first group of postcursor taps is a selected intersymbol interference estimate.

3. The method of claim 1, wherein said step of precomputing said partial intersymbol interference estimates for a given group of postcursor taps further comprises the step of combining a (i) partial intersymbol interference estimate for a previous group of postcursor taps, and (ii) a combination of products of channel coefficients and possible symbol values for each tap of said plurality of postcursor taps.

4. A signal processor for processing a signal received from a dispersive channel using a reduced-state sequence estimation technique, said channel having a channel impulse response, said signal processor comprising:

a decision feedback unit for precomputing partial intersymbol interference estimates for each of a plurality of postcursor taps of said channel impulse response, wherein said precomputed partial intersymbol interference estimates are based on each possible value for a data symbol;

a multiplexer for selecting a precomputed partial intersymbol interference estimate for each of said plurality of postcursor taps based on a past decision from a corresponding state, wherein a selected partial intersymbol interference estimate for a first postcursor tap is a selected intersymbol interference estimate;

a branch metrics unit for computing a branch metric based on said selected intersymbol interference estimate; and

an add-compare-select unit for computing a new path metric for a path extension from a corresponding state based on said branch metric and determining a best survivor path into a state by selecting a path having a best new path metric among said corresponding computed new path metrics.

5. The signal processor of claim 4, wherein said decision feedback unit selects a precomputed partial intersymbol interference estimate for a group of said plurality of postcursor taps based on past decisions, wherein a selected partial intersymbol interference estimate for a first group of postcursor taps is a selected intersymbol interference estimate.

6. The signal processor of claim 4, wherein said decision feedback unit precomputes said partial intersymbol interference estimates for a given group of postcursor taps is further configured to combine a (i) partial intersymbol interference estimate for a previous group of postcursor taps, and (ii) a combination of products of channel coefficients and possible symbol values for each tap of said plurality of postcursor taps.

7. An apparatus for processing a signal received from a dispersive channel using a reduced-state sequence estimation technique, said channel having a channel impulse response, said apparatus comprising:

a memory; and

at least one processor, coupled to the memory, operative to;

precompute partial intersymbol interference estimates for each of a plurality of postcursor taps of said channel impulse response, wherein said precomputed partial intersymbol interference estimates are based on each possible value for a data symbol;

select a precomputed partial intersymbol interference estimate for each of said plurality of postcursor taps based on a past decision from a corresponding state, wherein a selected partial intersymbol interference estimate for a first postcursor tap is a selected intersymbol interference estimate;

compute a branch metric based on said selected intersymbol interference estimate;

compute a new path metric for a path extension from a corresponding state based on said branch metric; and

determine a best survivor path into a state by selecting a path having a best new path metric among said corresponding computed new path metrics.

8. The apparatus of claim 7, wherein said first selecting step comprises the step of selecting a precomputed partial intersymbol interference estimate for a group of said plurality of postcursor taps based on past decisions, wherein a selected partial intersymbol interference estimate for a first group of postcursor taps is a selected intersymbol interference estimate.

9. The apparatus of claim 7, wherein said step of precomputing said partial intersymbol interference estimates for a given group of postcursor taps further comprises the step of combining a (i) partial intersymbol interference estimate for a previous group of postcursor taps, and (ii) a combination of products of channel coefficients and possible symbol values for each tap of said plurality of postcursor taps.