Method and apparatus for time-frequency domain forward error correction for digital communication systems

• US 6,976,202 B1
• Filed: 03/11/2002
• Issued: 12/13/2005
• Est. Priority Date: 03/09/2001
• Status: Expired due to Term

• Current Assignee: Ikanos Communications Incorporated (Qualcomm, Inc.)
• Original Assignee: Ikanos Communications Incorporated (Qualcomm, Inc.)
• Inventors: Ginis, George, Rezvani, Behrooz
• Primary Examiner(s): Chase, Shelly
• Assistant Examiner(s): ABRAHAM, ESAW T
• Application Number:
  US10/095,618
• Time in Patent Office: 1,373 Days
• Field of Search: 714/776, 714/758, 714/786, 714/752, 375/222
• US Class Current: 714/752
• CPC Class Codes: H03M 13/2957 Turbo codes and decoding
• CPC Class Codes: H03M 13/3776 using a re-encoding step during the decoding process
• CPC Class Codes: H04L 1/0042 Encoding specially adapted to other signal generation operation, e.g. in order to reduce transmit distortions, jitter, or to improve signal shape H04L1/0067 takes precedence
• CPC Class Codes: H04L 1/005 Iterative decoding, including iteration between signal detection and decoding operation
• CPC Class Codes: H04L 1/0057 Block codes H04L1/0061, H04L1/0064 take precedence
• CPC Class Codes: H04L 1/0066 Parallel concatenated codes
• CPC Class Codes: H04L 1/04 using frequency diversity
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT

Abstract

A method and apparatus for time and frequency domain forward error correction (FEC) in a modem which communicates data using multiple discrete sub-channels is provided. The invention may be implemented in hardware, software or firmware. In an embodiment of the invention a modem with a plurality of components forming a transmit path and a receive path is disclosed. The modem communicates data across a wired or wireless communication medium using a multiplicity of discrete sub-channels. The modem includes a transform component and a time domain FEC component. The transform component transforms the multiplicity of discrete sub-channels of a communication between a time domain and a frequency domain on the receive path and vice-versa on the transmit path. The time domain FEC component couples to the transform component. The time domain FEC component has a complementary encoder and decoder portion on the transmit and receive paths respectively. The encoder and decoder portions encode and decode respectively the multiplicity of discrete sub-channels in the time domain.

Claims

1. A modem with a plurality of components forming a transmit path and a receive path for communicating data across a communication medium using a multiplicity of discrete sub-channels, and the modem comprising:

a first forward error correction (FEC) component with complementary encoder and decoder portions on the transmit path and receive paths respectively, and with the complementary encoder and decoder portions encoding and decoding respectively the multiplicity of discrete sub-channels in a frequency domain;

second FEC component with complementary encoder and decoder portions on the transmit and receive paths respectively, and with the complement encoder and decoder portions encoding and decoding respectively the multiplicity of discrete sub-channels in a time domain; and

a Fourier transform component coupled between the first and second FEC, and the transform component for transforming the multiplicity of discrete sub-channels of a communication between the time domain and the frequency domain on the receive path and vice-versa on the transmit path.

2. The modem of claim 1, further comprising;

the first FEC encoder adding a first set of redundant bits into the multiplicity of discrete sub-channels in the frequency domain; and

the second FEC encoder adding a second set of redundant bits into the multiplicity of discrete sub-channels in the time domain.

3. The modem of claim 1, further comprising:

a re-encoder switchably coupled between the complementary encoder portion of the second FEC component and the complementary encoder portion of the first FEC component, to form a feedback loop for iterative re-encoding and de-coding of received data, to improve reliability of the decoding of received data.

4. The modem of claim 1, wherein the second FEC further comprises:

the encoder portion on the transmit path including;

a threshold detector to detect levels above a threshold level in signals transmitted by the modem; and

logic coupled with the threshold detector and with the Fourier transform component to accept binary data corresponding with the sub-channels transmitted in the time domain from the Fourier transform component and to add a redundant bit to the binary data with the redundant bit matching a most significant bit of the binary data and complementing the most significant bit of the binary data depending on signal levels detected by the threshold detector; and

the decoder portion on the receive path including;

a parser to parse the redundant bit from binary data corresponding with each of the sub-channels received in the time domain.

5. The modem of claim 1, comprises at least one of a physical modem and a logical modem.

6. The modem of claim 1, wherein the at least one of the first and second FEC components further comprises:

complementary encoder and decoder portions exhibit a selected one of;

a block type, a state machine type and a turbo type.

7. The modem of claim 1, wherein the discrete sub-channels established over the communication medium exhibits at least one of:

a discrete multi-tone (DMT) and an orthogonal frequency division multiplexed (OFDM) communication protocol.

8. The modem of claim 1, wherein the communication medium comprises one of a wired medium and a wireless medium.

9. A method for forward error correction (FEC) in a modem with a transmit path and a receive path for communicating data across a communication medium using a multiplicity of discrete sub-channels, and the method comprising:

on the transmit path the steps of;

performing a first FEC encoding on transmitted sub-channels in a frequency domain;

transforming the transmitted sub-channels encoded in the first performing step on the transmit path between the frequency domain and the time domain; and

performing a second FEC encoding in the time domain of the transmitted sub-channels transformed in the transforming step on the transmit path.

10. The method of claim 9, further comprising the steps performed on the receive path of;

performing a first FEC decoding of received sub-channels in the time domain;

transforming the multiplicity of discrete sub-channels encoded in the first performing step on the receive path between the time domain and the frequency domain; and

performing a second FEC decoding in the frequency domain of the received sub-channels transformed in the transforming act on the receive path.

11. The method of claim 10, further comprising the additional steps performed on the receive path of;

re-encoding in both the time domain and the frequency domain the received sub-channels de-coded on the receive path in the first and second performing steps; and

subjecting the received sub-channels re-encoded in the re-encoding step to at least an other round of the first and second performing steps on the receive path to improve reliability of the decoding of the received sub-channels.

12. The method of claim 10, wherein the second performing step on the receive path further comprises

parsing on the receive path of the modem a redundant bit from binary data corresponding with each of the received sub-channels in the time domain.

13. The method of claim 9, wherein the second performing step on the transmit path further comprises;

detecting levels above a threshold level value in signals transmitted by the modem on the transmit path; and

adding a redundant bit to binary data corresponding with each of the sub-channels in the time domain transformed in the transforming step on the transmit path and with the redundant bit matching a most significant bit of the binary data and complementing the most significant bit of the binary data depending on the signal levels detected in the detecting act step.

14. The method of claim 9, wherein the at least one of the first and second performing steps further comprises at least one of the steps of:

performing an FEC encoding of a block type;

performing an FEC encoding of a state machine type; and

performing an FEC encoding of a turbo type.

15. The method of claim 9, wherein the discrete sub-channels established over the communication medium exhibits at least one of:

a discrete multi-tone (DMT) and an orthogonal frequency division multiplexed (OFDM) communication protocol.

16. The method of claim 9, wherein the communication medium comprises one of a wired medium and a wireless medium.

17. A means for forward error correction (FEC) in a modem with a transmit path and a receive path for communicating data across a communication medium using a multiplicity of discrete sub-channels, and the means comprising:

on the transmit path;

means for performing a first FEC encoding on transmitted sub-channels in a frequency domain;

means for transforming the sub-channels encoded by the means for performing the first FEC encoding between the frequency domain and a time domain; and

means for performing a second FEC encoding in the time domain the transmitted sub-channels transformed by the means for transforming.

18. The means for FEC of claim 17, further comprising on the receive path;

means for performing a first FEC decoding on received sub-channels in the time domain;

means for transforming the sub-channels encoded by the means for performing the first FEC decoding on the receive path between the time domain and the frequency domain; and

means for performing a second FEC decoding in the frequency domain on the received sub-channels transformed by the means for transforming on the receive path.

19. The means for FEC of claim 18, further comprising on the receive path;

means for re-encoding in the time domain and the frequency domain the received sub-channels de-coded on the receive path by the means for performing the first and second FEC; and

means for subjecting the received sub-channels re-encoded in the means for re-encoding to at least an other round of the decoding performed by the means for performing the first and second FEC on the receive path to improve reliability of the decoding of the received sub-channels.