An Error Correction Technique For The Wireless Channel Using Speech Codec

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An Error Correction Technique For The Wireless
Channel Using Speech Codec
2008.02.18 Youkyung Oh
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System block diagram
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Speech codec

• Speech codec
• Waveform coders
• PCM ( Pulse Code Modulation )
• Vocoders
• LPC ( Linear Predictive Coding)
• Hybrid coders
• CELP ( Code Excited Linear Prediction )
• QCELP ( Qualcomm Code Excited Linear Prediction )
• EVRC ( Enhanced Variable Rate Coding )
• CS-ACELP ( Conjugate-Structure Algebraic CELP )
• CS-ACELP
• Encoder encoder.exe
• Ex) C\encoder enc_input.bin enc_output.bin
• Decoder decoder.exe
• Ex) C\decoder dec_input.bin dec_output.bin

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Cyclic Redundancy Check

• CRC

Frame check sequence
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Cyclic Redundancy Check

• CRC encoder
• General CRC circuit when divisor is
• 80bits(10byte) 8bits
• Notice that we should only encode important 40
  bits
• Error Correction with CRC
• Do Nothing, Insert Silence, Parameter Repeat,
  Parameter Interpolation

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Convolutional Code

• Parameters
• code rate k/n, constraint Length K
• k input, n output with K registers

K3, code rate 1/2
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Convolutional Code

• State Diagram Trellis Diagram

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Convolutional Code

• Decoder Trellis diagram (1/2, K3)

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Convolutional Code

• Viterbi Decoding
• Select a survivor at time 4

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Interleaver

• 4 X 6 Block Interleaver

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Channel
p - 1

• Binary Symmetry Model
• P(01)P(10)p
• P(00)P(11)1-p
• Jakes model makes consecutive errors

0
0
p
p
1
1
p - 1
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Prelab/Reference

• Prelab
• Explain the advantage and disadvantage of three
  speech codecs
• What is the difference of CS-ACELP codec from
  CELP codec?
• Explain fading
• Investigate another decoding schemes of
  convolutional codes
• Why do we use a interleaver? What is the
  adequate length of the interleaver in general
  fading channels
• Investigate another interleaving schemes
• Reference
• Fred Halsall, Data Communications, Computer
  Networks and Open Systems
• Sklar, Digital Communications, Prentice-Hall
• J. G. Proakis, Digital Communications, Prentice
  Hall, 2001, 4th ed
• Shu Lin, Daniel J. Costello, Error Control
  Coding, Prentice-Hall