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Error Correction Technique for Wireless Channel Using Speech Codec

This paper presents an error correction technique for the wireless channel using a speech codec. It discusses the block diagram of the system, speech codec types, cyclic redundancy check, convolutional code, interleaving, fading, and decoding schemes of convolutional codes.

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Error Correction Technique for Wireless Channel Using Speech Codec

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  1. An Error Correction Technique For The Wireless Channel Using Speech Codec 2008.02.18 Youkyung Oh

  2. 8kHz CELP Encoder Input Speech 8kbps 8.8kbps Convolutional Sampling CRC Encoder (Source Interleaver Code and 16 bit Coding) Quantize Channel Output CRC Check and Convolutional Speech Filtering Deinterleaver CELP Decoder Error Frame Code Decoding Correction System block diagram

  3. 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

  4. Cyclic Redundancy Check • CRC : Frame check sequence

  5. 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

  6. Convolutional Code • Parameters • code rate = k/n, constraint Length = K • k input, n output with K registers K=3, code rate = 1/2

  7. input 0 input 1 00 Output branch word a=00 11 11 00 Encoder b=10 c=01 State 10 01 01 Input bit 0 d=11 Input bit 1 10 Convolutional Code • State Diagram & Trellis Diagram

  8. Convolutional Code • Decoder Trellis diagram (1/2, K=3)

  9. Convolutional Code • Viterbi Decoding • Select a survivor at time 4

  10. Interleaver • 4 X 6 Block Interleaver

  11. Channel p - 1 • Binary Symmetry Model • P(0|1)=P(1|0)=p • P(0|0)=P(1|1)=1-p • Jake’s model makes consecutive errors 0 0 p p 1 1 p - 1

  12. 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

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