Turbo decoder with decision feedback equalization

• US 6,307,901 B1
• Filed: 04/24/2000
• Issued: 10/23/2001
• Est. Priority Date: 04/24/2000
• Status: Expired due to Term

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Tan, Ming, Zhu, Mang, Yu, Xiaoyong
• Primary Examiner(s): TSE, YOUNG TOI
• Application Number:
  US09/563,064
• Time in Patent Office: 547 Days
• Field of Search: 375/233, 375/262, 375/265, 375/340, 375/341, 375/346, 375/348, 714/755, 714/759, 714/760, 714/774, 714/786, 714/794, 714/795
• US Class Current: 375/341
• CPC Class Codes: H03M 13/2957 Turbo codes and decoding
• CPC Class Codes: H03M 13/3905 Maximum a posteriori probability [MAP] decoding or approximations thereof based on trellis or lattice decoding, e.g. forward-backward algorithm, log-MAP decoding, max-log-MAP decoding
• CPC Class Codes: H03M 13/6331 Error control coding in combination with equalisation
• CPC Class Codes: H04L 1/005 Iterative decoding, including iteration between signal detection and decoding operation
• CPC Class Codes: H04L 1/0066 Parallel concatenated codes
• CPC Class Codes: H04L 1/0068 by puncturing
• CPC Class Codes: H04L 25/03057 with a recursive structure H04L25/03031 takes precedence

Abstract

A decoder equalizes a turbo coded signal with intersymbol interference by performing a decision-feedback equalization in each iteration of the turbo decoding process. In such iteration process, two recursion processors calculate soft output values for the information bits and the coded bits of the signal as well. Hard output values are derived from the soft output values. A decision feedback equalizer in an iterative loop of the decoder receives the hard output values uses these to provide a correction for the intersymbol interference. Thereafter, the decision feedback signal applies the correction signal to the input signal to minimize the intersymbol interference.

Claims

1. A decoder that provides intersymbol interference equalization in decoding a received turbo coded signal, the decoder comprising:

a turbo decoder with two recursion processors connected in an iterative loop, the turbo decoder for decoding information and coded bits of the signal; and

an equalizer feedback loop coupled to the turbo decoder and adapted to receive hard decision values for the coded and information bits from the turbo decoder, the feedback loop includes a decision feedback equalizer that inputs the hard decision values along with estimates for channel characteristics derived and updated from the previous frame to calculate an intersymbol interference correction signal, the decision feedback signal applies a correction to the next input of the signal before being input to the turbo decoder so as to minimize the intersymbol interference.

2. The decoder of claim 1, wherein the equalizer is implemented in an iterative loop of the turbo decoder, and the values applied to the equalizer are calculated in each turbo decoding iteration.

3. The decoder of claim 1, wherein the coded bits are parity bits.

4. The decoder of claim 1, wherein the recursion processors use a decoding algorithm including one of the group of a MAP, MAP derivatives, SOVA, and Viterbi algorithm.

5. The decoder of claim 1, wherein the recursion processors use a LLR value calculated for the coded bits to derive a hard decision value that is applied to the equalizer.

6. The decoder of claim 5, wherein the LLR coefficients for the information bits are used in the LLR calculation for the corresponding coded bits.

7. A decoder that provides intersymbol interference equalization for a received turbo coded signal, the decoder comprising:

a turbo decoder with two recursion processors connected in an iterative loop, the turbo decoder for decoding information and coded bits of the received turbo coded signal; and

an iterative equalizer feedback loop coupled to the turbo decoder and adapted to receive hard decision values for the coded and information bits calculated in each turbo decoding iteration from the turbo decoder, the feedback loop includes a decision feedback equalizer that inputs the hard decision values along with estimates for channel characteristics derived and updated from the previous frame to calculate an intersymbol interference correction signal, the decision feedback equalizer applies the intersymbol interference correction signal to correct the next input of the received turbo coded signal before being input to the turbo decoder so as to minimize the intersymbol interference.

8. The decoder of claim 7, wherein the coded bits are parity bits.

9. The decoder of claim 7, wherein the recursion processors use a decoding algorithm including one of the group of a MAP, MAP derivatives, SOVA, and Viterbi algorithm.

10. The decoder of claim 7, wherein the recursion processors use a LLR value calculated for the coded bits to derive a hard decision value that is applied to the equalizer.

11. The decoder of claim 10, wherein the LLR coefficients for the information bits are used in the LLR calculation for the corresponding coded bits.

12. The decoder of claim 7, wherein the equalizer of the feedback operates on multiplexed and interleaved symbols constructed from the hard decisions of the coded and information bits to provide an equalization signal that is subsequently summed with the input signal and deinterleaved before application to the turbo decoder.

13. A method of equalizing intersymbol interference in a received turbo coded signal using decision feedback equalization, the method comprising the steps of:

providing a turbo decoder with two recursion processors connected in an iterative loop, the turbo decoder for decoding information and coded bits of the received turbo coded signal and calculating soft output values for the information bits and coded bits of the received turbo coded signal;

calculating hard decision values for the soft output values from the turbo decoder;

determining and updating intersymbol interference equalization coefficients from the hard decision values;

applying the equalization coefficients to multiplexed and interleaved hard decision values to provide a correction signal; and

equalizing the intersymbol interference of the received turbo coded signal using the correction signal from the applying step.

14. The method of claim 13, wherein the providing, calculating, determining, applying and equalizing steps occur synchronously in said iterative loop.

15. The method of claim 13, wherein the coded bits of the providing step are parity bits.

16. The method of claim 13, wherein the providing step include decoding information using one of the iterative algorithms of the group of a MAP, MAP derivatives, SOVA, and Viterbi algorithms.

17. The method of claim 13, wherein the providing step includes calculating a LLR value for the coded bits.

18. The method of claim 17, wherein the providing step includes calculating said LLR value for the information bits and using those LLR coefficients calculated for the information bits to calculate a LLR value for the coded bits.