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III. Turbo Codes

III. Turbo Codes. Summary MAP Algorithm. Forward Recursive Equation. Backward Recursive Equation. Iterative Decoding Principles. Note that. Iterative Decoding Principles. Iterative Decoding Principles. Iterative Decoding Principles. Define. Iterative Decoding Principles.

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III. Turbo Codes

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  1. III. Turbo Codes

  2. Summary MAP Algorithm Forward Recursive Equation Backward Recursive Equation

  3. Iterative Decoding Principles Note that

  4. Iterative Decoding Principles

  5. Iterative Decoding Principles

  6. Iterative Decoding Principles Define

  7. Iterative Decoding Principles

  8. Iterative Decoding Principles Le12 is called the extrinsic information generated by the first decoder for the second decoder

  9. Iterative Decoding Principles For the second decoder L1a N-bit De-Inter. L1[u|y] L2[u|y] L2a L12e MAP Decoder 1 N-bit Interleaver MAP Decoder 2 L21e - - y1p ys x x Lc Lc N-bit Interleaver N-bit De-Inter. u* y2p

  10. Performance of Iterative Decoding

  11. Performance of Iterative Decoding

  12. Max-Log-MAP Algorithm • The MAP algorithm requires exponential operation and storage. • Uses an approximation to reduce the computations of the summation of numerous exponentials • Max-log-MAP algorithm is a sub-optimum decoding algorithm • Gives a slight degradation in performance compared to the MAP algorithm. This degradation is about 0.35dB when used for iterative decoding of turbo codes • Approximation used

  13. Max-Log-MAP Algorithm Define

  14. Max-Log-MAP Algorithm The New Backwards Recursive Equation Approximation

  15. Max-Log-MAP Algorithm The New Forward Recursive Equation Approximation

  16. Max-Log-MAP Algorithm The New Forward Recursive Equation Approximation

  17. Effect on MAP Decoder Type

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