Modems, methods, and computer program products for identifying a signaling alphabet in variance with an ideal alphabet due to digital impairments

• US 6,389,064 B1
• Filed: 03/08/1999
• Issued: 05/14/2002
• Est. Priority Date: 03/08/1999
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Ware, Malcolm Scott, Neeser, Fredy D., Dholakia, Ajay, Eleftheriou, Evangelos Stavros, Fischer, Robert F. H.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): JIANG, LENNY R
• Application Number:
  US09/264,272
• Time in Patent Office: 1,163 Days
• Field of Search: 375/222, 375/219, 375/220, 375/232, 375/316, 708/322
• US Class Current: 375/222
• CPC Class Codes: H04L 2025/03363 Multilevel H04L2025/03369 takes precedence
• 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 25/061 providing hard decisions only; arrangements for tracking or suppressing unwanted low frequency components, e.g. removal of dc offset removal of dc offset in coupling arrangements H04L25/029, H04L25/0296
• CPC Class Codes: H04L 25/4927 using levels matched to the quantisation levels of the channel
• CPC Class Codes: H04L 5/16 Half-duplex systems; Simplex/duplex switching; Transmission of break signals non-automatically inverting the direction of transmission
• CPC Class Codes: H04L 7/0029 interpolation of received data signal
• CPC Class Codes: H04L 7/0062 detection of error based on data decision error, e.g. Mueller type detection

Abstract

Modems, methods, and computer program products identify a signaling alphabet that is in variance with an ideal alphabet due to digital impairments and is used to decode received data symbols. In particular, a set of alphabet thresholds are established that correspond to the data symbols. The data symbols are received in an equalizer, which generates output symbols in response thereto. A collection of data symbols corresponding to a particular alphabet threshold are accumulated and an average value is computed, which is then used to replace the current value for the particular alphabet threshold to which the average value corresponds. Equalizer performance is enhanced as the improved accuracy of the alphabet thresholds results in better error information being fed back for adapting the equalizer filter coefficients.

Claims

1. A method for identifying a signaling alphabet used by a modem receiver to decode transmitted symbols, comprising the steps of:

establishing a plurality of alphabet thresholds corresponding to valid transmitted symbols;

receiving the transmitted symbols in an equalizer and generating output symbols in response thereto;

computing an average value for the output symbols corresponding to a particular alphabet threshold; and

updating the particular alphabet threshold with the average value.

2. A method as recited in claim 1, further comprising the step of repeating the computing and updating steps for each of the plurality of alphabet thresholds.

3. A method as recited in claim 1, further comprising the step of adjusting, responsive to the receiving step and prior to the computing and updating steps, a set of filter coefficients for the equalizer, the adjusting step being performed at a first frequency.

4. A method as recited in claim 3, wherein the adjusting step is further performed at a second frequency in parallel with the computing and updating steps.

5. A method as recited in claim 4, wherein the second frequency is less than the first frequency.

6. A method as recited in claim 1, wherein the plurality of alphabet thresholds comprises pulse amplitude modulation (PAM) levels.

7. A modem having a signaling alphabet identification capability for decoding transmitted symbols, comprising:

means for establishing a plurality of alphabet thresholds corresponding to valid transmitted symbols;

means for receiving the transmitted symbols in an equalizer and generating output symbols in response thereto;

means for computing an average value for each of the output symbols corresponding to the plurality of alphabet thresholds; and

means for updating the alphabet thresholds with their corresponding average values.

8. A modem as recited in claim 7, further comprising means for adjusting, responsive to the means for receiving, a set of filter coefficients for the equalizer at a first frequency, the means for computing and the means for updating being responsive to the means for adjusting.

9. A modem as recited in claim 8, wherein the means for adjusting operates at a second frequency in parallel with the means for computing and the means for updating.

10. A modem as recited in claim 9, wherein the second frequency is less than the first frequency.

11. A modem as recited in claim 7, wherein the plurality of alphabet thresholds comprises pulse amplitude modulation (PAM) levels.

12. A computer program product for identifying a signaling alphabet used by a modem receiver to decode transmitted symbols, comprising:

a computer readable storage medium having computer readable program code means embodied therein, the computer readable code means comprising;

logic configured to establish a plurality of alphabet thresholds corresponding to valid transmitted symbols;

logic configured to receive the transmitted symbols in an equalizer and generate output symbols in response thereto;

logic configured to compute an average value for each of the output symbols corresponding to the plurality of alphabet thresholds; and

logic configured to update the alphabet thresholds with their corresponding average values.

13. A computer program product as recited in claim 12, further comprising logic configured to adjust, responsive to the logic configured to receive, a set of filter coefficients for the equalizer at a first frequency, the logic configured to compute and the logic configured to update being responsive to the logic configured to adjust.

14. A computer program product as recited in claim 13, wherein the logic configured to adjust operates at a second frequency in parallel with the logic configured to compute and the logic configured to update.

15. A computer program product as recited in claim 14, wherein the second frequency is less than the first frequency.

16. A computer program product as recited in claim 12, wherein the plurality of alphabet thresholds comprises pulse amplitude modulation (PAM) levels.